Welcome to Knot DNS's documentation!


What is Knot DNS

Knot DNS is a high-performance open-source DNS server. It implements only the authoritative domain name service. Knot DNS can reliably serve TLD domains as well as any other zones.

Knot DNS benefits from its multi-threaded and mostly lock-free implementation which allows it to scale well on SMP systems and operate non-stop even when adding or removing zones.

The server itself is accompanied by several utilities for general DNS operations or for maintaining the server.

For more info and downloads see www.knot-dns.cz.

Knot DNS features

DNS features:

  • Primary and secondary server operation

  • Internet class (IN)

  • DNS extension (EDNS0, EDE)

  • TCP and UDP protocols

  • Zone catalog generation and interpretation

  • Minimal responses

  • Dynamic zone updates

  • DNSSEC with NSEC and NSEC3

  • ZONEMD generation and validation

  • Transaction signature using TSIG

  • Full and incremental zone transfers (AXFR, IXFR)

  • Name server identification using NSID or Chaos TXT records


Server features:

  • IPv4 and IPv6 support

  • Semantic zone checks

  • Server control interface

  • Zone journal storage

  • Persistent zone event timers

  • YAML-based or database-based configuration

  • Query processing modules with dynamic loading

  • On-the-fly zone management and server reconfiguration

  • Multithreaded DNSSEC zone signing and zone validation

  • Automatic DNSSEC key management

  • Zone data backup and restore

  • Offline KSK operation

  • PKCS #11 interface

Remarkable module extensions:

  • Response rate limiting

  • Forward and reverse records synthesis

  • DNS request traffic statistics

  • Efficient DNS traffic logging interface

  • Dnstap traffic logging

  • Online DNSSEC signing

  • GeoIP response tailoring supporting ECS and DNSSEC

Remarkable supported networking features:

  • TCP Fast Open (client and server)

  • High-performance UDP and TCP through AF_XDP processing (on Linux 4.18+)

  • SO_REUSEPORT (on Linux) or SO_REUSEPORT_LB (on FreeBSD 12.0+) on UDP and by choice on TCP

  • Binding to non-local addresses (IP_FREEBIND on Linux, IP_BINDANY/IPV6_BINDANY on FreeBSD)

  • Ignoring PMTU information for IPv4/UDP via IP_PMTUDISC_OMIT


Knot DNS is licensed under the GNU General Public License version 3 or (at your option) any later version. The full text of the license is available in the COPYING file distributed with source code.



Knot DNS requirements are not very demanding for typical installations, and a commodity server or a virtual solution will be sufficient in most cases.

However, please note that there are some scenarios that will require administrator's attention and some testing of exact requirements before deploying Knot DNS to a production environment. These cases include deployment for a large number of zones (DNS hosting), large number of records in one or more zones (TLD), or large number of requests.

CPU requirements

The server scales with processing power and also with the number of available cores/CPUs. Enabling Hyper-threading is convenient if supported.

There is no lower bound on the CPU requirements, but it should support memory barriers and atomic instructions (i586 and newer).

Network card

The best results have been achieved with multi-queue network cards. The number of multi-queues should equal the total number of CPU cores (with Hyper-threading enabled).

Memory requirements

The server implementation focuses on performance and thus can be quite memory demanding. The rough estimate for memory requirements is 3 times the size of the zone in the plain-text format. Again this is only an estimate and you are advised to do your own measurements before deploying Knot DNS to production.


To ensure uninterrupted serving of the zone, Knot DNS employs the Read-Copy-Update mechanism instead of locking and thus requires twice the amount of memory for the duration of incoming transfers.

Operating system

Knot DNS itself is written in a portable way and can be compiled and run on most UNIX-like systems, such as Linux, *BSD, and macOS.

Required libraries

Knot DNS requires a few libraries to be available:

  • libedit

  • gnutls >= 3.3

  • liburcu >= 0.5.4

  • lmdb >= 0.9.15


The LMDB library is included with Knot DNS source code. However, linking with the system library is preferred.

Optional libraries

International Domain Names support (IDNA2008 or IDNA2003) in kdig:

  • libidn2 (or libidn)

Systemd's startup notification mechanism and journald logging:

  • libsystemd

Dnstap support in kdig or module dnstap:

  • fstrm (and protobuf-c if building from source code)

Linux capabilities(7) support, which allows the server to be started as a non-root user/group, binding to privileged ports (53), and giving up all its capabilities, resulting in a completely unprivileged process:

  • libcap-ng >= 0.6.4

MaxMind database for geodb support in module geoip:

  • libmaxminddb0

DNS-over-HTTPS (DoH) support in kdig:

  • libnghttp2

The XDP functionality and kxdpgun tool. These are only supported on Linux operating systems. See the chapter Mode XDP for software and hardware recommendations.

  • libbpf >= 0.0.6

  • libmnl (for kxdpgun)


Installation from a package

Knot DNS may already be included in your operating system distribution and therefore can be installed from packages (Linux), ports (BSD), or via Homebrew (macOS). This is always preferred unless you want to test the latest features, contribute to Knot development, or you know what you are doing.

See the project download page for the latest information.

Installation from source code

Required build environment

The build process relies on these standard tools:

  • make

  • libtool

  • pkg-config

  • autoconf >= 2.65

  • python-sphinx (optional, for documentation building)

GCC >= 4.1 is mandatory for atomic built-ins, but the latest available version is recommended. Another requirement is _GNU_SOURCE and C99 support, otherwise it adapts to the available compiler features. LLVM clang compiler since version 2.9 can be used as well.

Getting the source code

You can find the source code for the latest release on www.knot-dns.cz. Alternatively, you can fetch the whole project from the git repository https://gitlab.nic.cz/knot/knot-dns.git.

After obtaining the source code, compilation and installation is quite a straightforward process using autotools.

Configuring and generating Makefiles

If compiling from git source, you need to bootstrap the ./configure file first:

$ autoreconf -i -f

In most cases, you can just run configure without any options:

$ ./configure

For all available configure options run:

$ ./configure --help


After running ./configure you can compile Knot DNS by running make command, which will produce binaries and other related files:

$ make


The compilation with enabled optimizations may take a long time. In such a case the --disable-fastparser configure option can help.


When you have finished building Knot DNS, it's time to install the binaries and configuration files into the operation system hierarchy. You can do so by executing:

$ make install

When installing as a non-root user, you might have to gain elevated privileges by switching to root user, e.g. sudo make install or su -c 'make install'.


Simple configuration

The following example presents a simple configuration file which can be used as a base for your Knot DNS setup:

# Example of a very simple Knot DNS configuration.

    listen: ::@53

  - domain: example.com
    storage: /var/lib/knot/zones/
    file: example.com.zone

  - target: syslog
    any: info

Now let's walk through this configuration step by step:

  • The listen statement in the server section defines where the server will listen for incoming connections. We have defined the server to listen on all available IPv4 and IPv6 addresses, all on port 53.

  • The zone section defines the zones that the server will serve. In this case, we defined one zone named example.com which is stored in the zone file /var/lib/knot/zones/example.com.zone.

  • The log section defines the log facilities for the server. In this example, we told Knot DNS to send its log messages with the severity info or more serious to the syslog (or systemd journal).

For detailed description of all configuration items see Configuration Reference.

Zone templates

A zone template allows a single zone configuration to be shared among several zones. There is no inheritance between templates; they are exclusive. The default template identifier is reserved for the default template:

  - id: default
    storage: /var/lib/knot/master
    semantic-checks: on

  - id: signed
    storage: /var/lib/knot/signed
    dnssec-signing: on
    semantic-checks: on
    master: [master1, master2]

  - id: slave
    storage: /var/lib/knot/slave

  - domain: example1.com     # Uses default template

  - domain: example2.com     # Uses default template
    semantic-checks: off     # Override default settings

  - domain: example.cz
    template: signed
    master: master3          # Override masters to just master3

  - domain: example1.eu
    template: slave
    master: master1

  - domain: example2.eu
    template: slave
    master: master2


Each template option can be explicitly overridden in zone-specific configuration.

Access control list (ACL)

The Access control list is a list of rules specifying remotes which are allowed to send certain types of requests to the server. Remotes can be specified by a single IP address or a network subnet. A TSIG key can also be assigned (see keymgr on how to generate a TSIG key).

Without any ACL rules, all the actions are denied for the zone. Each ACL rule can allow one or more actions for a given address/subnet/TSIG, or deny them.

If there are multiple ACL rules for a single zone, they are applied in the order of appearance in the acl configuration item of a zone or a template. The first one to match the given remote is applied, the rest is ignored.

For dynamic updates, additional rules may be specified, which will allow or deny updates according to the type or owner of Resource Records in the update.

See the following examples and ACL section.

  - id: address_rule
    address: [2001:db8::1,]
    action: transfer

  - id: deny_rule
    action: transfer
    deny: on

  - domain: acl1.example.com.
    acl: [deny_rule, address_rule] # deny_rule first here to take precedence
  - id: key1                  # The real TSIG key name
    algorithm: hmac-md5
    secret: Wg==

  - id: deny_all
    deny: on # no action specified and deny on implies denial of all actions

  - id: key_rule
    key: key1                 # Access based just on TSIG key
    action: [transfer, notify]

  - domain: acl2.example.com
    acl: [deny_all, key_rule]
    - id: owner_type_rule
      action: update
      update-type: [A, AAAA, MX] # Updates are only allowed to update records of the specified types
      update-owner: name         # The allowed owners are specified by the list on the next line
      update-owner-name: [a, b.example.com.] # Non-FQDN names are relative to the effective zone name
      update-owner-match: equal  # The owners of records in an update must be exactly equal to the names in the list


If more conditions (address ranges and/or a key) are given in a single ACL rule, all of them have to be satisfied for the rule to match.


In order to restrict regular DNS queries, use module queryacl.

Secondary (slave) zone

Knot DNS doesn't strictly differ between primary (formerly known as master) and secondary (formerly known as slave) zones. The only requirement for a secondary zone is to have a master statement set. Also note that you need to explicitly allow incoming zone changed notifications via notify action through a zone's acl list, otherwise the update will be rejected by the server. If the zone file doesn't exist it will be bootstrapped over AXFR:

  - id: master
    # via:            # Specify local source address if needed

  - id: notify_from_master
    action: notify

  - domain: example.com
    storage: /var/lib/knot/zones/
    # file: example.com.zone   # Default value
    master: master
    acl: notify_from_master

Note that the master option accepts a list of multiple remotes. The remotes should be listed according to their preference. The first remote has the highest preference, the other remotes are used for failover. When the server receives a zone update notification from a listed remote, that remote will be the most preferred one for the subsequent transfer.

To use TSIG for transfers and notification messages authentication, configure a TSIG key and assign the key both to the remote and the ACL rule. Notice that the remote and ACL definitions are independent:

  - id: slave1_key
    algorithm: hmac-md5
    secret: Wg==

  - id: master
    key: slave1_key

  - id: notify_from_master
    key: slave1_key
    action: notify


When transferring a lot of zones, the server may easily get into a state where all available ports are in the TIME_WAIT state, thus transfers cease until the operating system closes the ports for good. There are several ways to work around this:

  • Allow reusing of ports in TIME_WAIT (sysctl -w net.ipv4.tcp_tw_reuse=1)

  • Shorten TIME_WAIT timeout (tcp_fin_timeout)

  • Increase available local port count

Primary (master) zone

An ACL with the transfer action must be configured to allow outgoing zone transfers. An ACL rule consists of a single address or a network subnet:

  - id: slave1

  - id: slave1_acl
    action: transfer

  - id: others_acl
    action: transfer

  - domain: example.com
    storage: /var/lib/knot/zones/
    file: example.com.zone
    notify: slave1
    acl: [slave1_acl, others_acl]

Optionally, a TSIG key can be specified:

  - id: slave1_key
    algorithm: hmac-md5
    secret: Wg==

  - id: slave1
    key: slave1_key

  - id: slave1_acl
    key: slave1_key
    action: transfer

  - id: others_acl
    action: transfer

Note that a secondary zone may serve as a primary zone at the same time:

  - id: master
  - id: slave1

  - id: notify_from_master
    action: notify

  - id: slave1_acl
    action: transfer

  - id: others_acl
    action: transfer

  - domain: example.com
    storage: /var/lib/knot/zones/
    file: example.com.zone
    master: master
    notify: slave1
    acl: [notify_from_master, slave1_acl, others_acl]

Dynamic updates

Dynamic updates for the zone are allowed via proper ACL rule with the update action. If the zone is configured as a secondary and a DNS update message is accepted, the server forwards the message to its primary master. The primary master's response is then forwarded back to the originator.

However, if the zone is configured as a primary, the update is accepted and processed:

  - id: update_acl
    action: update

  - domain: example.com
    file: example.com.zone
    acl: update_acl

Automatic DNSSEC signing

Knot DNS supports automatic DNSSEC signing of zones. The signing can operate in two modes:

  1. Automatic key management. In this mode, the server maintains signing keys. New keys are generated according to assigned policy and are rolled automatically in a safe manner. No zone operator intervention is necessary.

  2. Manual key management. In this mode, the server maintains zone signatures only. The signatures are kept up-to-date and signing keys are rolled according to timing parameters assigned to the keys. The keys must be generated and timing parameters must be assigned by the zone operator.

The DNSSEC signing process maintains some metadata which is stored in the KASP database. This database is backed by LMDB.


Make sure to set the KASP database permissions correctly. For manual key management, the database must be readable by the server process. For automatic key management, it must be writeable. If no HSM is used, the database also contains private key material – don't set the permissions too weak.

Automatic ZSK management

For automatic ZSK management a signing policy has to be configured and assigned to the zone. The policy specifies how the zone is signed (i.e. signing algorithm, key size, key lifetime, signature lifetime, etc.). If no policy is specified or the default one is assigned, the default signing parameters are used.

A minimal zone configuration may look as follows:

  - domain: myzone.test
    dnssec-signing: on

With a custom signing policy, the policy section will be added:

  - id: custom_policy
    signing-threads: 4
    algorithm: ECDSAP256SHA256
    zsk-lifetime: 60d

  - domain: myzone.test
    dnssec-signing: on
    dnssec-policy: custom_policy

After configuring the server, reload the changes:

$ knotc reload

The server will generate initial signing keys and sign the zone properly. Check the server logs to see whether everything went well.

Automatic KSK management

For automatic KSK management, first configure ZSK management like above, and use additional options in policy section, mostly specifying desired (finite) lifetime for KSK:

  - id: parent_zone_server

  - id: parent_zone_sbm
    parent: [parent_zone_server]

  - id: custom_policy
    signing-threads: 4
    algorithm: ECDSAP256SHA256
    zsk-lifetime: 60d
    ksk-lifetime: 365d
    ksk-submission: parent_zone_sbm

  - domain: myzone.test
    dnssec-signing: on
    dnssec-policy: custom_policy

After the initially-generated KSK reaches its lifetime, new KSK is published and after convenience delay the submission is started. The server publishes CDS and CDNSKEY records and the user shall propagate them to the parent. The server periodically checks for DS at the parent zone and when positive, finishes the rollover.

Manual key management

For automatic DNSSEC signing with manual key management, a signing policy with manual key management flag has to be set:

  - id: manual
    manual: on

  - domain: myzone.test
    dnssec-signing: on
    dnssec-policy: manual

To generate signing keys, use the keymgr utility. For example, we can use Single-Type Signing:

$ keymgr myzone.test. generate algorithm=ECDSAP256SHA256 ksk=yes zsk=yes

And reload the server. The zone will be signed.

To perform a manual rollover of a key, the timing parameters of the key need to be set. Let's roll the key. Generate a new key, but do not activate it yet:

$ keymgr myzone.test. generate algorithm=ECDSAP256SHA256 ksk=yes zsk=yes active=+1d

Take the key ID (or key tag) of the old key and disable it the same time the new key gets activated:

$ keymgr myzone.test. set <old_key_id> retire=+2d remove=+3d

Reload the server again. The new key will be published (i.e. the DNSKEY record will be added into the zone). Remember to update the DS record in the parent zone to include a reference to the new key. This must happen within one day (in this case) including a delay required to propagate the new DS to caches.


If you ever decide to switch from manual key management to automatic key management, note that the automatic key management uses zsk-lifetime and ksk-lifetime policy configuration options to schedule key rollovers and it internally uses timestamps of keys differently than in the manual case. As a consequence it might break if the retire or remove timestamps are set for the manually generated keys currently in use. Make sure to set these timestamps to zero using keymgr:

$ keymgr myzone.test. set <key_id> retire=0 remove=0

and configure your policy suitably according to Automatic ZSK management and Automatic KSK management.

Zone signing

The signing process consists of the following steps:

  1. Processing KASP database events. (e.g. performing a step of a rollover).

  2. Updating the DNSKEY records. The whole DNSKEY set in zone apex is replaced by the keys from the KASP database. Note that keys added into the zone file manually will be removed. To add an extra DNSKEY record into the set, the key must be imported into the KASP database (possibly deactivated).

  3. Fixing the NSEC or NSEC3 chain.

  4. Removing expired signatures, invalid signatures, signatures expiring in a short time, and signatures issued by an unknown key.

  5. Creating missing signatures. Unless the Single-Type Signing Scheme is used, DNSKEY records in a zone apex are signed by KSK keys and all other records are signed by ZSK keys.

  6. Updating and re-signing SOA record.

The signing is initiated on the following occasions:

  • Start of the server

  • Zone reload

  • Reaching the signature refresh period

  • Key set changed due to rollover event

  • Received DDNS update

  • Forced zone re-sign via server control interface

On a forced zone re-sign, all signatures in the zone are dropped and recreated.

The knotc zone-status command can be used to see when the next scheduled DNSSEC re-sign will happen.

On-secondary (on-slave) signing

It is possible to enable automatic DNSSEC zone signing even on a secondary server. If enabled, the zone is signed after every AXFR/IXFR transfer from primary, so that the secondary always serves a signed up-to-date version of the zone.

It is strongly recommended to block any outside access to the primary server, so that only the secondary server's signed version of the zone is served.

Enabled on-secondary signing introduces events when the secondary zone changes while the primary zone remains unchanged, such as a key rollover or refreshing of RRSIG records, which cause inequality of zone SOA serial between primary and secondary. The secondary server handles this by saving the primary's SOA serial in a special variable inside KASP DB and appropriately modifying AXFR/IXFR queries/answers to keep the communication with primary server consistent while applying the changes with a different serial.

Catalog zones

Catalog zones are a concept whereby a list of zones to be configured is maintained as contents of a separate, special zone. This approach has the benefit of simple propagation of a zone list to secondary servers, especially when the list is frequently updated. Currently, catalog zones are described in this Internet Draft.

Terminology first. Catalog zone is a meta-zone which shall not be a part of the DNS tree, but it contains information about the set of member zones and is transferable to secondary servers using common AXFR/IXFR techniques. Catalog-member zone (or just member zone) is a zone based on information from the catalog zone and not from configuration file/database. Member properties are some additional information related to each member zone, also distributed by the catalog zone.

A catalog zone is handled almost in the same way as a regular zone: It can be configured using all the standard options (but for example DNSSEC signing would be useless), including primary/secondary configuration and ACLs. A catalog zone is indicated by setting the option catalog-role. The difference is that standard DNS queries to a catalog zone are answered with REFUSED as though the zone doesn't exist, unless querying over TCP from an address with transfers enabled by ACL. The name of the catalog zone is arbitrary. It's possible to configure multiple catalog zones.


Don't choose a name for a catalog zone below a name of any other existing zones configured on the server as it would effectively "shadow" part of your DNS subtree.

Upon catalog zone (re)load or change, all the PTR records in the format unique-id.zones.catalog. 0 IN PTR member.com. (but not too.deep.zones.catalog.!) are processed and member zones created, with zone names taken from the PTR records' RData, and zone settings taken from the configuration templates specified by catalog-template.

The owner names of the PTR records shall follow this scheme:


where the mentioned labels shall match:

  • <unique-id> — Single label that is recommended to be unique among member zones.

  • zones — Required label.

  • <catalog-zone> — Name of the catalog zone.

Additionally, records in the format group.unique-id.zones.catalog. 0 IN TXT "conf-template" are processed as a definition of the member's group property. The unique-id must match the one of the PTR record defining the member.

All other records and other member properties are ignored. They remain in the catalog zone, however, and might be for example transferred to a secondary server, which may interpret catalog zones differently. SOA still needs to be present in the catalog zone and its serial handled appropriately. An apex NS record should be present for the sake of interoperability. The version record version 0 IN TXT "2" is required at the catalog zone apex.

A catalog zone may be modified using any standard means (e.g. AXFR/IXFR, DDNS, zone file reload). In the case of incremental change, only affected member zones are reloaded.

The catalog zone must have at least one catalog-template configured. The configuration for any defined member zone is taken from its group property value, which should match some catalog-template name. If the group property is not defined for a member, is empty, or doesn't match any of defined catalog-template names, the first catalog-template (in the order from configuration) is used.

Any de-cataloged member zone is purged immediately, including its zone file, journal, timers, and DNSSEC keys. The zone file is not deleted if zonefile-sync is set to -1 for member zones. Any member zone, whose PTR record's owner has been changed, is purged immediately if and only if the <unique-id> has been changed.

When setting up catalog zones, it might be useful to set catalog-db and catalog-db-max-size to non-default values.


Whenever a catalog zone is updated, the server reloads itself with all configured zones, including possibly existing other catalog zones. It's similar to calling knotc zone-reload (for all zones). The consequence is that new zone files might be discovered and reloaded, even for zones that do not relate to updated catalog zone.


The server does not work well if one member zone appears in two catalog zones concurrently. The user is encouraged to avoid this situation whatsoever. Thus, there is no way a member zone can be migrated from one catalog to another while preserving its metadata. Following steps may be used as a workaround:

  • Back up the member zone's metadata (on each server separately).

  • Remove the member zone from the catalog it's a member of.

  • Wait for the catalog zone to be propagated to all servers.

  • Add the member zone to the other catalog.

  • Restore the backed up metadata (on each server separately).

Catalog zones configuration examples

Below are configuration snippets (e.g. server and log sections missing) of very simple catalog zone setups, in order to illustrate the relations between catalog-related configuration options.

First setup represents a very simple scenario where the primary is the catalog zone generator and the secondary is the catalog zone consumer.

Primary configuration:

  - id: slave_xfr
    address: ...
    action: transfer

  - id: mmemb
    catalog-role: member
    catalog-zone: catz.
    acl: slave_xfr

  - domain: catz.
    catalog-role: generate
    acl: slave_xfr

  - domain: foo.com.
    template: mmemb

  - domain: bar.com.
    template: mmemb

Secondary configuration:

  - id: master_notify
    address: ...
    action: notify

  - id: smemb
    master: master
    acl: master_notify

  - domain: catz.
    master: master
    acl: master_notify
    catalog-role: interpret
    catalog-template: smemb

When new zones are added (or removed) to the primary configuration with assigned mmemb template, they will automatically propagate to the secondary and have the smemb template assigned there.

Second example is with a hand-written (or script-generated) catalog zone, while employing configuration groups:

catz.                   0       SOA     invalid. invalid. 1625079950 3600 600 2147483646 0
catz.                   0       NS      invalid.
version.catz.           0       TXT     "2"
nj2xg5bnmz2w4ltd.zones.catz.       0       PTR     just-fun.com.
group.nj2xg5bnmz2w4ltd.zones.catz. 0       TXT     unsigned
nvxxezjnmz2w4ltd.zones.catz.       0       PTR     more-fun.com.
group.nvxxezjnmz2w4ltd.zones.catz. 0       TXT     unsigned
nfwxa33sorqw45bo.zones.catz.       0       PTR     important.com.
group.nfwxa33sorqw45bo.zones.catz. 0       TXT     signed
mjqw42zomnxw2lq0.zones.catz.       0       PTR     bank.com.
group.mjqw42zomnxw2lq0.zones.catz. 0       TXT     signed

And the server in this case is configured to distinguish the groups by applying different templates:

  - id: unsigned

  - id: signed
    dnssec-signing: on
    dnssec-policy: ...

  - domain: catz.
    file: ...
    catalog-role: interpret
    catalog-template: [ unsigned, signed ]

Query modules

Knot DNS supports configurable query modules that can alter the way queries are processed. Each query requires a finite number of steps to be resolved. We call this set of steps a query plan, an abstraction that groups these steps into several stages.

  • Before-query processing

  • Answer, Authority, Additional records packet sections processing

  • After-query processing

For example, processing an Internet-class query needs to find an answer. Then based on the previous state, it may also append an authority SOA or provide additional records. Each of these actions represents a 'processing step'. Now, if a query module is loaded for a zone, it is provided with an implicit query plan which can be extended by the module or even changed altogether.

A module is active if its name, which includes the mod- prefix, is assigned to the zone/template module option or to the default template global-module option if activating for all queries. If the module is configurable, a corresponding module section with an identifier must be created and then referenced in the form of module_name/module_id. See Modules for the list of available modules.


Query modules are processed in the order they are specified in the zone/template configuration. In most cases, the recommended order is:

mod-synthrecord, mod-onlinesign, mod-cookies, mod-rrl, mod-dnstap, mod-stats

Performance Tuning

Numbers of Workers

There are three types of workers ready for parallel execution of performance-oriented tasks: UDP workers, TCP workers, and Background workers. The first two types handle all network requests via the UDP and TCP protocol (respectively) and do the response jobs for common queries. Background workers process changes to the zone.

By default, Knot determines a well-fitting number of workers based on the number of CPU cores. The user can specify the number of workers for each type with configuration/server section: udp-workers, tcp-workers, background-workers.

An indication of when to increase the number of workers is when the server is lagging behind expected performance, while CPU usage remains low. This is usually due to waiting for network or I/O response during the operation. It may be caused by Knot design not fitting the use-case well. The user should try increasing the number of workers (of the related type) slightly above 100 and if the performance improves, decide a further, exact setting.

Number of available file descriptors

A name server configured for a large number of zones (hundreds or more) needs enough file descriptors available for zone transfers and zone file updates, which default OS settings often don't provide. It's necessary to check with the OS configuration and documentation and ensure the number of file descriptors (sometimes called a number of concurrently open files) effective for the knotd process is set suitably high. The number of concurrently open incoming TCP connections must be taken into account too. In other words, the required setting is affected by the tcp-max-clients setting.

Sysctl and NIC optimizations

There are several recommendations based on Knot developers' experience with their specific HW and SW (mainstream Intel-based servers, Debian-based GNU/Linux distribution). They may improve or impact performance in common use cases.

If your NIC driver allows it (see /proc/interrupts for hint), set CPU affinity (/proc/irq/$IRQ/smp_affinity) manually so that each NIC channel is served by unique CPU core(s). You must turn off irqbalance service in advance to avoid configuration override.

Configure sysctl as follows:


net.core.wmem_max     = $socket_bufsize
net.core.wmem_default = $socket_bufsize
net.core.rmem_max     = $socket_bufsize
net.core.rmem_default = $socket_bufsize
net.core.busy_read = $busy_latency
net.core.busy_poll = $busy_latency
net.core.netdev_max_backlog = $backlog
net.core.optmem_max = $optmem_max

Disable huge pages.

Configure your CPU to "performance" mode. This can be achieved depending on architecture, e.g. in BIOS, or e.g. configuring /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor to "performance".

Tune your NIC device with ethtool:

ethtool -A $dev autoneg off rx off tx off
ethtool -K $dev tso off gro off ufo off
ethtool -G $dev rx 4096 tx 4096
ethtool -C $dev rx-usecs 75
ethtool -C $dev tx-usecs 75
ethtool -N $dev rx-flow-hash udp4 sdfn
ethtool -N $dev rx-flow-hash udp6 sdfn

On FreeBSD you can just:

ifconfig ${dev} -rxcsum -txcsum -lro -tso

Knot developers are open to hear about users' further suggestions about network devices tuning/optimization.


The Knot DNS server part knotd can run either in the foreground, or in the background using the -d option. When run in the foreground, it doesn't create a PID file. Other than that, there are no differences and you can control both the same way.

The tool knotc is designed as a user front-end, making it easier to control a running server daemon. If you want to control the daemon directly, use SIGINT to quit the process or SIGHUP to reload the configuration.

If you pass neither configuration file (-c parameter) nor configuration database (-C parameter), the server will first attempt to use the default configuration database stored in /var/lib/knot/confdb or the default configuration file stored in /etc/knot/knot.conf. Both the default paths can be reconfigured with --with-storage=path or --with-configdir=path respectively.

Example of server start as a daemon:

$ knotd -d -c knot.conf

Example of server shutdown:

$ knotc -c knot.conf stop

For a complete list of actions refer to the program help (-h parameter) or to the corresponding manual page.

Also, the server needs to create rundir and storage directories in order to run properly.

Configuration database

In the case of a huge configuration file, the configuration can be stored in a binary database. Such a database can be simply initialized:

$ knotc conf-init

or preloaded from a file:

$ knotc conf-import input.conf

Also the configuration database can be exported into a textual file:

$ knotc conf-export output.conf


The import and export commands access the configuration database directly, without any interaction with the server. Therefore, any data not yet committed to the database won't be exported. And the server won't reflect imported configuration correctly. So it is strictly recommended to import new configuration when the server is not running.

Dynamic configuration

The configuration database can be accessed using the server control interface while the server is running. To get the full power of the dynamic configuration, the server must be started with a specified configuration database location or with the default database initialized. Otherwise all the changes to the configuration will be temporary (until the server is stopped).


The database can be imported in advance.

Most of the commands get an item name and value parameters. The item name is in the form of section[identifier].name. If the item is multivalued, more values can be specified as individual (command line) arguments.


Beware of the possibility of pathname expansion by the shell. For this reason, it is advisable to escape (with backslash) square brackets or to quote command parameters if not executed in the interactive mode.

To get the list of configuration sections or to get the list of section items:

$ knotc conf-list
$ knotc conf-list 'server'

To get the whole configuration or to get the whole configuration section or to get all section identifiers or to get a specific configuration item:

$ knotc conf-read
$ knotc conf-read 'remote'
$ knotc conf-read 'zone.domain'
$ knotc conf-read 'zone[example.com].master'


The following operations don't work on OpenBSD!

Modifying operations require an active configuration database transaction. Just one transaction can be active at a time. Such a transaction then can be aborted or committed. A semantic check is executed automatically before every commit:

$ knotc conf-begin
$ knotc conf-abort
$ knotc conf-commit

To set a configuration item value or to add more values or to add a new section identifier or to add a value to all identified sections:

$ knotc conf-set 'server.identity' 'Knot DNS'
$ knotc conf-set 'server.listen' '' '::@53'
$ knotc conf-set 'zone[example.com]'
$ knotc conf-set 'zone.slave' 'slave2'


Also the include operation can be performed. A non-absolute file location is relative to the server binary path, not to the control binary path!

$ knotc conf-set 'include' '/tmp/new_zones.conf'

To unset the whole configuration or to unset the whole configuration section or to unset an identified section or to unset an item or to unset a specific item value:

$ knotc conf-unset
$ knotc conf-unset 'zone'
$ knotc conf-unset 'zone[example.com]'
$ knotc conf-unset 'zone[example.com].master'
$ knotc conf-unset 'zone[example.com].master' 'remote2' 'remote5'

To get the change between the current configuration and the active transaction for the whole configuration or for a specific section or for a specific identified section or for a specific item:

$ knotc conf-diff
$ knotc conf-diff 'zone'
$ knotc conf-diff 'zone[example.com]'
$ knotc conf-diff 'zone[example.com].master'


While it is possible to change most of the configuration parameters dynamically or via configuration file reload, a few of the parameters in the section server require restarting the server, such that the changes take effect. These parameters are: rundir, user, pidfile, tcp-reuseport, udp-workers, tcp-workers, background-workers, and listen.

An example of possible configuration initialization:

$ knotc conf-begin
$ knotc conf-set 'server.listen' '' '::@53'
$ knotc conf-set 'remote[master_server]'
$ knotc conf-set 'remote[master_server].address' ''
$ knotc conf-set 'template[default]'
$ knotc conf-set 'template[default].storage' '/var/lib/knot/zones/'
$ knotc conf-set 'template[default].master' 'master_server'
$ knotc conf-set 'zone[example.com]'
$ knotc conf-diff
$ knotc conf-commit

Secondary (slave) mode

Running the server as a secondary server is very straightforward as you usually bootstrap zones over AXFR and thus avoid any manual zone operations. In contrast to AXFR, when the incremental transfer finishes, it stores the differences in the journal file and doesn't update the zone file immediately but after the zonefile-sync period elapses.

Primary (master) mode

If you just want to check the zone files before starting, you can use:

$ knotc zone-check example.com

Reading and editing zones

Knot DNS allows you to read or change zone contents online using the server control interface.


Avoid concurrent zone access when a zone event (zone file load, refresh, DNSSEC signing, dynamic update) is in progress or pending. In such a case zone events must be frozen before. For more information on how to freeze the zone read Reading and editing the zone file safely.

To get contents of all configured zones, or a specific zone contents, or zone records with a specific owner, or even with a specific record type:

$ knotc zone-read --
$ knotc zone-read example.com
$ knotc zone-read example.com ns1
$ knotc zone-read example.com ns1 NS


If the record owner is not a fully qualified domain name, then it is considered as a relative name to the zone name.

To start a writing transaction on all zones or on specific zones:

$ knotc zone-begin --
$ knotc zone-begin example.com example.net

Now you can list all nodes within the transaction using the `zone-get` command, which always returns current data with all changes included. The command has the same syntax as `zone-read`.

Within the transaction, you can add a record to a specific zone or to all zones with an open transaction:

$ knotc zone-set example.com ns1 3600 A
$ knotc zone-set -- ns1 3600 A

To remove all records with a specific owner, or a specific rrset, or specific record data:

$ knotc zone-unset example.com ns1
$ knotc zone-unset example.com ns1 A
$ knotc zone-unset example.com ns1 A

To see the difference between the original zone and the current version:

$ knotc zone-diff example.com

Finally, either commit or abort your transaction:

$ knotc zone-commit example.com
$ knotc zone-abort example.com

A full example of setting up a completely new zone from scratch:

$ knotc conf-begin
$ knotc conf-set zone.domain example.com
$ knotc conf-commit
$ knotc zone-begin example.com
$ knotc zone-set example.com @ 7200 SOA ns hostmaster 1 86400 900 691200 3600
$ knotc zone-set example.com ns 3600 A
$ knotc zone-set example.com www 3600 A
$ knotc zone-commit example.com


If quotes are necessary for record data specification, remember to escape them:

$ knotc zone-set example.com @ 3600 TXT \"v=spf1 a:mail.example.com -all\"

Reading and editing the zone file safely

It's always possible to read and edit zone contents via zone file manipulation. It may lead to confusion, however, if the zone contents are continuously being changed by DDNS, DNSSEC signing and the like. In such a case, the safe way to modify the zone file is to freeze zone events first:

$ knotc -b zone-freeze example.com.
$ knotc -b zone-flush example.com.

After calling freeze on the zone, there still may be running zone operations (e.g. signing), causing freeze pending. Because of this, the blocking mode is used to ensure the operation was finished. Then the zone can be flushed to a file.

Now the zone file can be safely modified (e.g. using a text editor). If zonefile-load is not set to difference-no-serial, it's also necessary to increase SOA serial in this step to keep consistency. Finally, we can load the modified zone file and if successful, thaw the zone:

$ knotc -b zone-reload example.com.
$ knotc zone-thaw example.com.

Zone loading

The process of how the server loads a zone is influenced by the configuration of the zonefile-load and journal-content parameters (also DNSSEC signing applies), the existence of a zone file and journal (and their relative out-of-dateness), and whether it is a cold start of the server or a zone reload (e.g. invoked by the knotc interface). Please note that zone transfers are not taken into account here – they are planned after the zone is loaded (including AXFR bootstrap).

If the zone file exists and is not excluded by the configuration, it is first loaded and according to its SOA serial number, relevant journal changesets are applied. If this is a zone reload and we have zonefile-load set to difference, the difference between old and new contents is computed and stored in the journal like an update. The zone file should be either unchanged since last load or changed with incremented SOA serial. In the case of a decreased SOA serial, the load is interrupted with an error; if unchanged, it is increased by the server.

If the procedure described above succeeds without errors, the resulting zone contents are (after potential DNSSEC signing) used as the new zone.

The option journal-content set to all lets the server, beside better performance, keep track of the zone contents also across server restarts. It makes the cold start effectively work like a zone reload with the old contents loaded from the journal (unless this is the very first start with the zone not yet saved into the journal).

Journal behaviour

The zone journal keeps some history of changes made to the zone. It is useful for responding to IXFR queries. Also if zone file flush is disabled, the journal keeps the difference between the zone file and the current zone in case of server shutdown. The history is stored in changesets – differences of zone contents between two (usually subsequent) zone versions (specified by SOA serials).

Journals of all zones are stored in a common LMDB database. Huge changesets are split into 70 KiB 1 blocks to prevent fragmentation of the DB. The journal does each operation in one transaction to keep consistency of the DB and performance.

Each zone journal has its own occupation limits maximum usage and maximum depth. Changesets are stored in the journal one by one. When hitting any of the limits, the zone is flushed into the zone file if there are no redundant changesets to delete, and the oldest changesets are deleted. In the case of the size limit, twice 1 the needed amount of space is purged to prevent overly frequent deletes.

If zone file flush is disabled, then instead of flushing the zone, the journal tries to save space by merging the changesets into a special one. This approach is effective if the changes rewrite each other, e.g. periodically changing the same zone records, re-signing the whole zone etc. Thus the difference between the zone file and the zone is still preserved even if the journal deletes some older changesets.

If the journal is used to store both zone history and contents, a special changeset is present with zone contents. When the journal gets full, the changes are merged into this special changeset.

There is also a safety hard limit for overall journal database size, but it's strongly recommended to set the per-zone limits in a way to prevent hitting this one. For LMDB, it's hard to recover from the database-full state. For wiping one zone's journal, see knotc zone-purge +journal command.


This constant is hardcoded.

Handling zone file, journal, changes, serials

Some configuration options regarding the zone file and journal, together with operation procedures, might lead to unexpected results. This chapter points out potential interference and both recommends and warns before some combinations thereof. Unfortunately, there is no optimal combination of configuration options, every approach has some disadvantages.

Example 1

Keep the zone file updated:

zonefile-sync: 0
zonefile-load: whole
journal-content: changes

These are default values. The user can always check the current zone contents in the zone file, and also modify it (recommended with server turned-off or taking the safe way). The journal serves here just as a source of history for secondary servers' IXFR. Some users dislike that the server overwrites their prettily prepared zone file.

Example 2

Zonefileless setup:

zonefile-sync: -1
zonefile-load: none
journal-content: all

Zone contents are stored only in the journal. The zone is updated by DDNS, zone transfer, or via the control interface. The user might have filled the zone contents initially from a zone file by setting zonefile-load to whole temporarily. It's also a good setup for secondary servers. Anyway, it's recommended to carefully tune the journal-size-related options to avoid surprises like the journal getting full.

Example 3

Input-only zone file:

zonefile-sync: -1
zonefile-load: difference
journal-content: changes

The user can make changes to the zone by editing the zone file, and his pretty zone file is never overwritten or filled with DNSSEC-related autogenerated records – they are only stored in the journal.

The zone file's SOA serial must be properly set to a number which is higher than the current SOA serial in the zone (not in the zone file) if manually updated!

Example 4

Auto-increment SOA serial:

zonefile-sync: -1
zonefile-load: difference-no-serial
journal-content: all

This is similar to the previous setup, but the SOA serial is handled by the server automatically. So the user no longer needs to care about it in the zone file.

However, this requires setting journal-content to all so that the information about the last real SOA serial is preserved in case of server re-start.

DNSSEC key states

During its lifetime, a DNSSEC key finds itself in different states. Most of the time it is used for signing the zone and published in the zone. In order to exchange the key, one type of a key rollover is necessary, and during this rollover, the key goes through various states with respect to the rollover type and also the state of the other key being rolled-over.

First, let's list the states of the key being rolled-in.

Standard states:

  • active — The key is used for signing.

  • published — The key is published in the zone, but not used for signing. If the key is a KSK or CSK, it is used for signing the DNSKEY RRSet.

  • ready (only for KSK) — The key is published in the zone and used for signing. The old key is still active, since we are waiting for the DS records in the parent zone to be updated (i.e. "KSK submission").

Special states for algorithm rollover:

  • pre-active — The key is not yet published in the zone, but it's used for signing the zone.

  • published — The key is published in the zone, and it's still used for signing since the pre-active state.

Second, we list the states of the key being rolled-out.

Standard states:

  • retire-active — The key is still used for signing, and is published in the zone, waiting for the updated DS records in parent zone to be acked by resolvers (KSK case) or synchronizing with KSK during algorithm rollover (ZSK case).

  • retired — The key is no longer used for signing. If ZSK, the key is still published in the zone.

  • removed — The key is not used in any way (in most cases such keys are deleted immediately).

Special states for algorithm rollover:

  • post-active — The key is no longer published in the zone, but still used for signing.

Special states for RFC 5011 trust anchor roll-over

  • revoke (only for KSK) — The key is published and used for signing, and the Revoked flag is set.


Trust anchor roll-over is not implemented with automatic key management.

The revoke state can only be established using keymgr when using Manual key management.

The states listed above are relevant for keymgr operations like generating a key, setting its timers and listing KASP database.

Note that the key "states" displayed in the server log lines while zone signing are not according to those listed above, but just a hint as to what the key is currently used for (e.g. "public, active" = key is published in the zone and used for signing).

DNSSEC key rollovers

This section describes the process of DNSSEC key rollover and its implementation in Knot DNS, and how the operator might watch and check that it's working correctly. The prerequisite is automatic zone signing with enabled automatic key management.

The KSK and ZSK rollovers are triggered by the respective zone key getting old according to the settings (see KSK and ZSK lifetimes).

The algorithm rollover starts when the policy algorithm field is updated to a different value.

The signing scheme rollover happens when the policy signing scheme field is changed.

It's also possible to change the algorithm and signing scheme in one rollover.

The operator may check the next rollover phase time by watching the next zone signing time, either in the log or via knotc zone-status. There is no special log for finishing a rollover.


There are never two key rollovers running in parallel for one zone. If a rollover is triggered while another is in progress, it waits until the first one is finished.

The ZSK rollover is performed with Pre-publish method, KSK rollover uses Double-Signature scheme, as described in RFC 6781.

Automatic KSK and ZSK rollovers example

Let's start with the following set of keys:

2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, key, tag 50613, algorithm ECDSAP256SHA256, KSK, public, active
2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active

The last fields hint the key state: public denotes a key that will be presented as the DNSKEY record, ready means that CDS/CDNSKEY records were created, active tells us that the key is used for signing, while active+ is an active key undergoing a roll-over or roll-in.

For demonstration purposes, the following configuration is used:

 - id: test_submission
   check-interval: 2s
   parent: dnssec_validating_resolver

 - id: test_policy
   ksk-lifetime: 5m
   zsk-lifetime: 2m
   propagation-delay: 2s
   dnskey-ttl: 10s
   zone-max-ttl: 15s
   ksk-submission: test_submission

Upon the zone's KSK lifetime expiration, a new KSK is generated and the rollover continues along the lines of RFC 6781#section-4.1.2:

# KSK Rollover (50613 -> 9081)

2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, signing zone
2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, KSK rollover started
2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, key, tag 50613, algorithm ECDSAP256SHA256, KSK, public, active
2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active
2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, key, tag  9081, algorithm ECDSAP256SHA256, KSK, public, active+
2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, signing started
2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, successfully signed
2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:50:12+0200

... (propagation-delay + dnskey-ttl) ...

2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, signing zone
2021-05-10T20:50:12+0200 notice: [example.com.] DNSSEC, KSK submission, waiting for confirmation
2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, key, tag 50613, algorithm ECDSAP256SHA256, KSK, public, active
2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active
2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, key, tag  9081, algorithm ECDSAP256SHA256, KSK, public, ready, active+
2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, signing started
2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, successfully signed
2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, next signing at 2021-05-17T20:49:56+0200

At this point the new KSK has to be submitted to the parent zone. Knot detects the updated parent's DS record automatically (and waits for additional period of the DS's TTL before retiring the old key) if parent DS check is configured, otherwise the operator must confirm it manually (using knotc zone-ksk-submitted):

2021-05-10T20:50:12+0200 info: [example.com.] DS check, outgoing, remote, KSK submission check: negative
2021-05-10T20:50:14+0200 info: [example.com.] DS check, outgoing, remote, KSK submission check: negative
2021-05-10T20:50:16+0200 info: [example.com.] DS check, outgoing, remote, KSK submission check: positive
2021-05-10T20:50:16+0200 notice: [example.com.] DNSSEC, KSK submission, confirmed
2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, signing zone
2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, key, tag 50613, algorithm ECDSAP256SHA256, KSK, public, active+
2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active
2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, key, tag  9081, algorithm ECDSAP256SHA256, KSK, public, active
2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, signing started
2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, successfully signed
2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:50:23+0200

... (parent's DS TTL is 7 seconds) ...

2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, signing zone
2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active
2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, key, tag  9081, algorithm ECDSAP256SHA256, KSK, public, active
2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, signing started
2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, successfully signed
2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:51:56+0200

Upon the zone's ZSK lifetime expiration, a new ZSK is generated and the rollover continues along the lines of RFC 6781#section-4.1.1:

# ZSK Rollover (62932 -> 33255)

2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, signing zone
2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, ZSK rollover started
2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active
2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, key, tag  9081, algorithm ECDSAP256SHA256, KSK, public, active
2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, key, tag 33255, algorithm ECDSAP256SHA256, public
2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, signing started
2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, successfully signed
2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:52:08+0200

... (propagation-delay + dnskey-ttl) ...

2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, signing zone
2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public
2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, key, tag  9081, algorithm ECDSAP256SHA256, KSK, public, active
2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, key, tag 33255, algorithm ECDSAP256SHA256, public, active
2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, signing started
2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, successfully signed
2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:52:25+0200

... (propagation-delay + zone-max-ttl) ...

2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, signing zone
2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, key, tag  9081, algorithm ECDSAP256SHA256, KSK, public, active
2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, key, tag 33255, algorithm ECDSAP256SHA256, public, active
2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, signing started
2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, successfully signed
2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:54:08+0200
2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, signing zone

Further rollovers:

... (zsk-lifetime - propagation-delay - zone-max-ttl) ...

# Another ZSK Rollover (33255 -> 49526)

2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, signing zone
2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, ZSK rollover started
2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, key, tag  9081, algorithm ECDSAP256SHA256, KSK, public, active
2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, key, tag 33255, algorithm ECDSAP256SHA256, public, active
2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, key, tag 49526, algorithm ECDSAP256SHA256, public
2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, signing started
2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, successfully signed
2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:54:20+0200


# Another KSK Rollover (9081 -> 9179)

2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, signing zone
2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, KSK rollover started
2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, key, tag  9081, algorithm ECDSAP256SHA256, KSK, public, active
2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, key, tag 49526, algorithm ECDSAP256SHA256, public, active
2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, key, tag  9179, algorithm ECDSAP256SHA256, KSK, public, active+
2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, signing started
2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, successfully signed
2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:55:12+0200



If systemd is available, the KSK submission event is logged into journald in a structured way. The intended use case is to trigger a user-created script. Example:

journalctl -f -t knotd -o json | python3 -c '
import json, sys
for line in sys.stdin:
  k = json.loads(line);
  if "KEY_SUBMISSION" in k:
    print("%s, zone=%s, keytag=%s" % (k["__REALTIME_TIMESTAMP"], k["ZONE"], k["KEY_SUBMISSION"]))


Knot DNS allows, with automatic DNSSEC key management, to configure a shared KSK for multiple zones. By enabling ksk-shared, we tell Knot to share all newly-created KSKs among all the zones with the same DNSSEC signing policy assigned.

The feature works as follows. Each zone still manages its keys separately. If a new KSK shall be generated for the zone, it first checks if it can grab another zone's shared KSK instead - that is the last generated KSK in any of the zones with the same policy assigned. Anyway, only the cryptographic material is shared, the key may have different timers in each zone.


If we have an initial setting with brand new zones without any DNSSEC keys, the initial keys for all zones are generated. With shared KSK, they will all have the same KSK, but different ZSKs. The KSK rollovers may take place at slightly different times for each of the zones, but the resulting new KSK will be shared again among all of them.

If we have zones which already have their keys, turning on the shared KSK feature triggers no action. But when a KSK rollover takes place, they will use the same new key afterwards.


Changing the policy id must be done carefully if shared KSK is in use.

DNSSEC delete algorithm

This is how to "disconnect" a signed zone from a DNSSEC-aware parent zone. More precisely, we tell the parent zone to remove our zone's DS record by publishing a special formatted CDNSKEY and CDS record. This is mostly useful if we want to turn off DNSSEC on our zone so it becomes insecure, but not bogus.

With automatic DNSSEC signing and key management by Knot, this is as easy as configuring cds-cdnskey-publish option and reloading the configuration. We check if the special CDNSKEY and CDS records with the rdata "0 3 0 AA==" and "0 0 0 00", respectively, appeared in the zone.

After the parent zone notices and reflects the change, we wait for TTL expire (so all resolvers' caches get updated), and finally we may do anything with the zone, e.g. turning off DNSSEC, removing all the keys and signatures as desired.


Knot DNS allows a special mode of operation where the private part of the Key Signing Key is not available to the daemon, but it is rather stored securely in an offline storage. This requires that the KSK/ZSK signing scheme is used (i.e. single-type-signing is off). The Zone Signing Key is always fully available to the daemon in order to sign common changes to the zone contents.

The server (or the "ZSK side") only uses ZSK to sign zone contents and its changes. Before performing a ZSK rollover, the DNSKEY records will be pre-generated and signed by the signer (the "KSK side"). Both sides exchange keys in the form of human-readable messages with the help of the keymgr utility.


For the ZSK side (i.e. the operator of the DNS server), the pre-requisites are:

For the KSK side (i.e. the operator of the KSK signer), the pre-requisites are:

  • Knot configuration equal to the ZSK side (at least relevant parts of corresponding policy, zone, and template sections must be identical)

  • a KASP DB with the KSK(s)

Generating and signing future ZSKs

  1. Use the keymgr pregenerate command on the ZSK side to prepare the ZSKs for a specified period of time in the future. The following example generates ZSKs for the example.com zone for 6 months ahead starting from now:

    $ keymgr -c /path/to/ZSK/side.conf example.com. pregenerate +6mo

    If the time period is selected as e.g. 2 x zsk-lifetime + 4 x propagation-delay, it will prepare roughly two complete future key rollovers. The newly-generated ZSKs remain in non-published state until their rollover starts, i.e. the time they would be generated in case of automatic key management.

  2. Use the keymgr generate-ksr command on the ZSK side to export the public parts of the future ZSKs in a form similar to DNSKEY records. You might use the same time period as in the first step:

    $ keymgr -c /path/to/ZSK/side.conf example.com. generate-ksr +0 +6mo > /path/to/ksr/file

    Save the output of the command (called the Key Signing Request or KSR) to a file and transfer it to the KSK side e.g. via e-mail.

  3. Use the keymgr sign-ksr command on the KSK side with the KSR file from the previous step as a parameter:

    $ keymgr -c /path/to/KSK/side.conf example.com. sign-ksr /path/to/ksr/file > /path/to/skr/file

    This creates all the future forms of the DNSKEY, CDNSKEY and CSK records and all the respective RRSIGs and prints them on output. Save the output of the command (called the Signed Key Response or SKR) to a file and transfer it back to the ZSK side.

  4. Use the keymgr import-skr command to import the records and signatures from the SKR file generated in the last step into the KASP DB on the ZSK side:

    $ keymgr -c /path/to/ZSK/side.conf example.com. import-skr /path/to/skr/file
  5. Use the knotc zone-keys-load command to trigger a zone re-sign on the ZSK-side and set up the future re-signing events correctly.:

    $ knotc -c /path/to/ZSK/side.conf zone-keys-load example.com.
  6. Now the future ZSKs and DNSKEY records with signatures are ready in KASP DB for later usage. Knot automatically uses them at the correct time intervals. The entire procedure must be repeated before the time period selected at the beginning passes, or whenever a configuration is changed significantly. Importing new SKR over some previously-imported one leads to deleting the old offline records.

Offline KSK and manual ZSK management

If the automatically preplanned ZSK roll-overs (first step) are not desired, just set the zsk-lifetime to zero, and manually pregenerate ZSK keys and set their timers. Then follow the steps generate-ksr sign-ksr import-skr zone-keys-load and repeat the ceremony when necessary.

Offline KSK roll-over

The KSKs (on the KSK side) must be managed manually, but manual KSK roll-over is possible. Just plan the steps of the KSK roll-over in advance, and whenever the KSK set or timers are changed, re-perform the relevant rest of the ceremony sign-ksr import-skr zone-keys-load.

Emergency SKR

A general recommendation for large deployments is to have some backup pre-published keys, so that if the current ones are compromised, they can be rolled-over to the backup ones without any delay. But in the case of Offline KSK, according to the procedures above, both ZSK and KSK immediate rollovers require the KSR-SKR ceremony.

However, a trick can be done to achieve really immediate key substitution. This is no longer about Knot DNS functionality, just a hint for the operator.

The idea is to perform every KSR-SKR ceremony twice: once with normal state of the keys (the backup key is only published), and once with the keys already exchanged (the backup key is temporarily marked as active and the standard key temporarily as public only). The second (backup) SKR should be saved for emergency key replacement.

Summary of the steps:

  • Prepare KSK and ZSK side as usual, including public-only emergency key

  • Perform normal Offline KSK ceremony:

    • Pre-generate ZSKs (only in the case of automatic ZSK management)

    • Generate KSR

    • Sign KSR on the KSK side

    • Import SKR

    • Re-sign the zone

  • Freeze the zone on the ZSK side

  • Temporarily set the backup key as active and the normal key as publish-only

  • Perform backup Offline KSK ceremony:

    • Generate KSR (only if the backup key is a replacement for ZSK)

    • Sign the KSR on the KSK side

    • Save the SKR to a backup storage, don't import it yet

  • Return the keys to the previous state

  • Thaw the zone on the ZSK side

Emergency key replacement:

  • Import the backup SKR

  • Align the keys with the new states (backup key as active, compromised key as public)

  • Re-sign the zone

Import of keys to HSM

Knot DNS stores DNSSEC keys in textual PEM format (RFC 7468), while many HSM management software require the keys for import to be in binary DER format (Rec. ITU-T X.690). Keys can be converted from one format to another by software tools such as certtool from GnuTLS suite or openssl from OpenSSL suite.

In the examples below, c4eae5dea3ee8c15395680085c515f2ad41941b6 is used as the key ID, c4eae5dea3ee8c15395680085c515f2ad41941b6.pem represents the filename of the key in PEM format as copied from the Knot DNS zone's KASP database directory, c4eae5dea3ee8c15395680085c515f2ad41941b6.priv.der represents the file containing the private key in DER format as generated by the conversion tool, and c4eae5dea3ee8c15395680085c515f2ad41941b6.pub.der represents the file containing the public key in DER format as generated by the conversion tool.

$ certtool -V -k --outder --infile c4eae5dea3ee8c15395680085c515f2ad41941b6.pem \
  --outfile c4eae5dea3ee8c15395680085c515f2ad41941b6.priv.der

$ certtool -V --pubkey-info --outder --load-privkey c4eae5dea3ee8c15395680085c515f2ad41941b6.pem \
  --outfile c4eae5dea3ee8c15395680085c515f2ad41941b6.pub.der

As an alternative, openssl can be used instead. It is necessary to specify either rsa or ec command according to the algorithm used by the key.

$ openssl rsa -outform DER -in c4eae5dea3ee8c15395680085c515f2ad41941b6.pem \
  -out c4eae5dea3ee8c15395680085c515f2ad41941b6.priv.der

$ openssl rsa -outform DER -in c4eae5dea3ee8c15395680085c515f2ad41941b6.pem \
  -out c4eae5dea3ee8c15395680085c515f2ad41941b6.pub.der -pubout

Actual import of keys (both public and private keys from the same key pair) to an HSM can be done via PKCS #11 interface, by pkcs11-tool from OpenSC toolkit for example. In the example below, /usr/local/lib/pkcs11.so is used as a name of the PKCS #11 library or module used for communication with the HSM.

$ pkcs11-tool --module /usr/local/lib/pkcs11.so --login \
  --write-object c4eae5dea3ee8c15395680085c515f2ad41941b6.priv.der --type privkey \
  --usage-sign --id c4eae5dea3ee8c15395680085c515f2ad41941b6

$ pkcs11-tool --module /usr/local/lib/pkcs11.so -login \
  --write-object c4eae5dea3ee8c15395680085c515f2ad41941b6.pub.der --type pubkey \
  --usage-sign --id c4eae5dea3ee8c15395680085c515f2ad41941b6

Daemon controls

Knot DNS was designed to allow server reconfiguration on-the-fly without interrupting its operation. Thus it is possible to change both configuration and zone files and also add or remove zones without restarting the server. This can be done with:

$ knotc reload

If you want to refresh the secondary zones, you can do this with:

$ knotc zone-refresh

Data and metadata backup

Some of the zone-related data, such as zone contents or DNSSEC signing keys, and metadata, like zone timers, might be worth backing up. For the sake of consistency, it's usually necessary to shut down the server, or at least freeze all the zones, before copying the data like zone files, KASP database, etc, to a backup location. To avoid this necessity, Knot DNS provides a feature to back up some or all of the zones seamlessly.

Online backup

While the server is running and the zones normally loaded (even when they are constantly/frequently being updated), the user can manually trigger the backup by calling:

$ knotc zone-backup +backupdir /path/of/backup

To back up just some of the zones (instead of all), the user might provide their list:

$ knotc zone-backup +backupdir /path/to/backup zone1.com. zone2.com. ...

The backup directory should be empty or non-existing and it must be accessible and writable for the user account under which knotd is running. The backup procedure will begin soon and will happen zone-by-zone (partially in parallel if more background-workers are configured). The user shall check the logs for the outcome of each zone's backup attempt. The knotc's -b parameter might be used if the user desires to wait until the backup work is done and a simple result status is printed out.


There is a plain ASCII text file in the backup directory, knot_backup.label, that contains some useful information about the backup, such as the backup creation date & time, the server identity, etc. Care must always be taken not to remove this file from the backup nor to damage it.

Offline restore

If the Online backup was performed for all zones, it's possible to restore the backed up data by simply copying them to their normal locations, since they're simply copies. For example, the user can copy (overwrite) the backed up KASP database files to their configured location.

This restore of course must be done when the server is stopped. After starting up the server, it should run in the same state as at the time of backup.

This method is recommended in the case of complete data loss, for example physical server failure.


The online backup procedure stores all zone files in a single directory using their default file names. If the original directory layout was different, then the required directory structure must be created manually for offline restore and zone files must be placed individually to their respective directories. If the zone file names don't follow the default pattern, they must be renamed manually to match the configuration. These limitations don't apply to the online restore procedure.

Online restore

This procedure is symmetrical to Online backup. By calling:

$ knotc zone-restore +backupdir /path/of/backup

the user triggers a one-by-one zone restore from the backup on a running server. Again, a subset of zones might be specified. It must be specified if the backup was created for only a subset of zones.


For restore of backups that have been created by Knot DNS releases prior to 3.1, it's necessary to use the -f option. Since this option also turns off some verification checks, it shouldn't be used in other cases.


Neither configuration file nor Configuration database is backed up by zone backup. The configuration has to be synchronized before zone restore is performed!

If the private keys are stored in a HSM (anything using a PKCS#11 interface), they are not backed up. This includes internal metadata of the PKCS#11 provider software, such as key mappings, authentication information, and the configuration of the provider. Details are vendor-specific.

The restore procedure does not care for keys deleted after taking the snapshot. Thus, after restore, there might remain some redundant .pem files of obsolete signing keys.


In order to seamlessly deploy a restored backup of KASP DB with respect to a possibly ongoing DNSSEC key rollover, it's recommended to set propagation-delay to the sum of:

  • The maximum delay between beginning of the zone signing and publishing re-signed zone on all public secondary servers.

  • How long it takes for the backup server to start up with the restored data.

  • The period between taking backup snapshots of the live environment.


The server provides some general statistics and optional query module statistics (see mod-stats).

Server statistics or global module statistics can be shown by:

$ knotc stats
$ knotc stats server             # Show all server counters
$ knotc stats mod-stats          # Show all mod-stats counters
$ knotc stats server.zone-count  # Show specific server counter

Per zone statistics can be shown by:

$ knotc zone-stats example.com mod-stats

To show all supported counters even with 0 value, use the force option.

A simple periodic statistic dump to a YAML file can also be enabled. See Statistics section for the configuration details.

As the statistics data can be accessed over the server control socket, it is possible to create an arbitrary script (Python is supported at the moment) which could, for example, publish the data in JSON format via HTTP(S) or upload the data to a more efficient time series database. Take a look into the python folder of the project for these scripts.

Mode XDP

Thanks to recent Linux kernel capabilities, namely eXpress Data Path and AF_XDP address family, Knot DNS offers a high-performance DNS over UDP packet processing mode. The basic idea is to filter DNS messages close to the network device and effectively forward them to the nameserver without touching the network stack of the operating system. Other messages (including DNS over TCP) are processed as usual.

If listen is configured, the server creates additional XDP workers, listening on specified interface(s) and port(s) for DNS over UDP queries. Each XDP worker handles one RX and TX network queue pair.


  • Linux kernel 4.18+ (5.x+ is recommended for optimal performance) compiled with the CONFIG_XDP_SOCKETS=y option. The XDP mode isn't supported in other operating systems.

  • A multiqueue network card, which offers enough Combined RX/TX channels, with native XDP support is highly recommended. Successfully tested cards:

    • Intel series 700 (driver i40e), maximum number of channels per interface is 64.

    • Intel series 500 (driver ixgbe), maximum number of channels per interface is 64. The number of CPUs available has to be at most 64!

  • If the knotd service is not directly executed in the privileged mode, some additional Linux capabilities have to be set:

    Execute command:

    systemctl edit knot

    And insert these lines:


    The CAP_SYS_RESOURCE is needed on Linux < 5.11.


Some helpful commands:

ethtool -N <interface> rx-flow-hash udp4 sdfn
ethtool -N <interface> rx-flow-hash udp6 sdfn
ethtool -L <interface> combined <?>
ethtool -G <interface> rx <?> tx <?>
renice -n 19 -p $(pgrep '^ksoftirqd/[0-9]*$')


  • VLAN segmentation is not supported.

  • Dynamic DNS over XDP is not supported.

  • MTU higher than 1792 bytes is not supported.

  • Multiple BPF filters per one network device are not supported.

  • Systems with big-endian byte ordering require special recompilation of the nameserver.

  • IPv4 header and UDP checksums are not verified on received DNS messages.

  • DNS over XDP traffic is not visible to common system tools (e.g. firewall, tcpdump etc.).

  • BPF filter is not automatically unloaded from the network device. Manual filter unload:

    ip link set dev <ETH> xdp off


First of all, check the logs. Enabling at least the warning message severity may help you to identify some problems. See the Logging section for details.

Reporting bugs

If you are unable to solve the problem by yourself, you can submit a bugreport to the Knot DNS developers. For security or sensitive issues contact the developers directly on knot-dns@labs.nic.cz. All other bugs and questions may be directed to the public Knot DNS users mailing list (knot-dns-users@lists.nic.cz) or may be entered into the issue tracking system.

Before anything else, please try to answer the following questions:

  • Has it been working?

  • What has changed? System configuration, software updates, network configuration, firewall rules modification, hardware replacement, etc.

The bugreport should contain the answers for the previous questions and in addition at least the following information:

  • Knot DNS version and type of installation (distribution package, from source, etc.)

  • Operating system, platform, kernel version

  • Relevant basic hardware information (processor, amount of memory, available network devices, etc.)

  • Description of the bug

  • Log output with the highest verbosity (category any, severity debug)

  • Steps to reproduce the bug (if known)

  • Backtrace (if the bug caused a crash or a hang; see the next section)

If possible, please provide a minimal configuration file and zone files which can be used to reproduce the bug.

Generating backtrace

Backtrace carries basic information about the state of the program and how the program got where it is. It helps determining the location of the bug in the source code.

If you run Knot DNS from distribution packages, make sure the debugging symbols for the package are installed. The symbols are usually distributed in a separate package.

There are several ways to get the backtrace. One possible way is to extract the backtrace from a core dump file. Core dump is a memory snapshot generated by the operating system when a process crashes. The generating of core dumps must be usually enabled:

$ ulimit -c unlimited                  # Enable unlimited core dump size
$ knotd ...                            # Reproduce the crash
$ gdb knotd <core-dump-file>           # Start gdb on the core dump
(gdb) info threads                     # Get a summary of all threads
(gdb) thread apply all bt full         # Extract backtrace from all threads
(gdb) quit

To save the backtrace into a file, the following GDB commands can be used:

(gdb) set pagination off
(gdb) set logging file backtrace.txt
(gdb) set logging on
(gdb) info threads
(gdb) thread apply all bt full
(gdb) set logging off

To generate a core dump of a running process, the gcore utility can be used:

$ gcore -o <output-file> $(pidof knotd)

Please note that core dumps can be intercepted by an error-collecting system service (systemd-coredump, ABRT, Apport, etc.). If you are using such a service, consult its documentation about core dump retrieval.

If the error is reproducible, it is also possible to start and inspect the server directly in the debugger:

$ gdb --args knotd -c /etc/knot.conf
(gdb) run

Alternatively, the debugger can be attached to a running server process. This is generally useful when troubleshooting a stuck process:

$ knotd ...
$ gdb --pid $(pidof knotd)
(gdb) continue

If you fail to get a backtrace of a running process using the previous method, you may try the single-purpose pstack utility:

$ pstack $(pidof knotd) > backtrace.txt

Configuration Reference


Configuration files for Knot DNS use simplified YAML format. Simplified means that not all of the features are supported.

For the description of configuration items, we have to declare a meaning of the following symbols:

  • INT – Integer

  • STR – Textual string

  • HEXSTR – Hexadecimal string (with 0x prefix)

  • BOOL – Boolean value (on/off or true/false)

  • TIME – Number of seconds, an integer with possible time multiplier suffix (s ~ 1, m ~ 60, h ~ 3600 or d ~ 24 * 3600)

  • SIZE – Number of bytes, an integer with possible size multiplier suffix (B ~ 1, K ~ 1024, M ~ 1024^2 or G ~ 1024^3)

  • BASE64 – Base64 encoded string

  • ADDR – IPv4 or IPv6 address

  • DNAME – Domain name

  • ... – Multi-valued item, order of the values is preserved

  • [ ] – Optional value

  • | – Choice

The configuration consists of several fixed sections and optional module sections. There are 15 fixed sections (module, server, xdp, control, log, statistics, database, keystore, key, remote, acl, submission, policy, template, zone). Module sections are prefixed with the mod- prefix (e.g. mod-stats).

Most of the sections (e.g. zone) are sequences of settings blocks. Each settings block begins with a unique identifier, which can be used as a reference from other sections (such an identifier must be defined in advance).

A multi-valued item can be specified either as a YAML sequence:

address: [,]

or as more single-valued items each on an extra line:


If an item value contains spaces or other special characters, it is necessary to enclose such a value within double quotes " ".


A comment begins with a # character and is ignored during processing. Also each configuration section or sequence block allows a permanent comment using the comment item which is stored in the server beside the configuration.


Another configuration file or files, matching a pattern, can be included at the top level in the current file. If the path is not absolute, then it is considered to be relative to the current file. The pattern can be an arbitrary string meeting POSIX glob requirements, e.g. dir/*.conf. Matching files are processed in sorted order.

include: STR

Module section

Dynamic modules loading configuration.


If configured with non-empty `--with-moduledir=path` parameter, all shared modules in this directory will be automatically loaded.

  - id: STR
    file: STR


A module identifier in the form of the mod- prefix and module name suffix.


A path to a shared library file with the module implementation.


If the path is not absolute, the library is searched in the set of system directories. See man dlopen for more details.

Default: ${libdir}/knot/modules-${version}/module_name.so (or ${path}/module_name.so if configured with --with-moduledir=path)

Server section

General options related to the server.

    identity: [STR]
    version: [STR]
    nsid: [STR|HEXSTR]
    rundir: STR
    user: STR[:STR]
    pidfile: STR
    udp-workers: INT
    tcp-workers: INT
    background-workers: INT
    async-start: BOOL
    tcp-idle-timeout: TIME
    tcp-io-timeout: INT
    tcp-remote-io-timeout: INT
    tcp-max-clients: INT
    tcp-reuseport: BOOL
    tcp-fastopen: BOOL
    remote-pool-limit: INT
    remote-pool-timeout: TIME
    remote-retry-delay: TIME
    socket-affinity: BOOL
    udp-max-payload: SIZE
    udp-max-payload-ipv4: SIZE
    udp-max-payload-ipv6: SIZE
    edns-client-subnet: BOOL
    answer-rotation: BOOL
    listen: ADDR[@INT] ...


When you change configuration parameters dynamically or via configuration file reload, some parameters in the Server section require restarting the Knot server so that the changes take effect. See below for the details.


An identity of the server returned in the response to the query for TXT record id.server. or hostname.bind. in the CHAOS class (RFC 4892). Set to an empty value to disable.

Default: FQDN hostname


A version of the server software returned in the response to the query for TXT record version.server. or version.bind. in the CHAOS class (RFC 4892). Set to an empty value to disable.

Default: server version


A DNS name server identifier (RFC 5001). Set to an empty value to disable.

Default: FQDN hostname at the moment of the daemon start


A path for storing run-time data (PID file, unix sockets, etc.).

Depending on the usage of this parameter, its change may require restart of the Knot server to take effect.

Default: ${localstatedir}/run/knot (configured with --with-rundir=path)


A system user with an optional system group (user:group) under which the server is run after starting and binding to interfaces. Linux capabilities are employed if supported.

Change of this parameter requires restart of the Knot server to take effect.

Default: root:root


A PID file location.

Change of this parameter requires restart of the Knot server to take effect.

Default: rundir/knot.pid


A number of UDP workers (threads) used to process incoming queries over UDP.

Change of this parameter requires restart of the Knot server to take effect.

Default: equal to the number of online CPUs


A number of TCP workers (threads) used to process incoming queries over TCP.

Change of this parameter requires restart of the Knot server to take effect.

Default: equal to the number of online CPUs, default value is at least 10


A number of workers (threads) used to execute background operations (zone loading, zone updates, etc.).

Change of this parameter requires restart of the Knot server to take effect.

Default: equal to the number of online CPUs, default value is at most 10


If enabled, server doesn't wait for the zones to be loaded and starts responding immediately with SERVFAIL answers until the zone loads.

Default: off


Maximum idle time (in seconds) between requests on an inbound TCP connection. It means if there is no activity on an inbound TCP connection during this limit, the connection is closed by the server.

Minimum: 1 s

Default: 10 s


Maximum time (in milliseconds) to receive or send one DNS message over an inbound TCP connection. It means this limit applies to normal DNS queries and replies, incoming DDNS, and outgoing zone transfers. The timeout is measured since some data is already available for processing. Set to 0 for infinity.

Default: 500 ms


In order to reduce the risk of Slow Loris attacks, it's recommended setting this limit as low as possible on public servers.


Maximum time (in milliseconds) to receive or send one DNS message over an outbound TCP connection which has already been established to a configured remote server. It means this limit applies to incoming zone transfers, sending NOTIFY, DDNS forwarding, and DS check or push. This timeout includes the time needed for a network round-trip and for a query processing by the remote. Set to 0 for infinity.

Default: 5000 ms


If enabled, each TCP worker listens on its own socket and the OS kernel socket load balancing is employed using SO_REUSEPORT (or SO_REUSEPORT_LB on FreeBSD). Due to the lack of one shared socket, the server can offer higher response rate processing over TCP. However, in the case of time-consuming requests (e.g. zone transfers of a TLD zone), enabled reuseport may result in delayed or not being responded client requests. So it is advisable to use this option on secondary servers.

Change of this parameter requires restart of the Knot server to take effect.

Default: off


If enabled, use TCP Fast Open for outbound TCP communication (client side): incoming zone transfers, sending NOTIFY, and DDNS forwarding. This mode simplifies TCP handshake and can result in better networking performance. TCP Fast Open for inbound TCP communication (server side) isn't affected by this configuration as it's enabled automatically if supported by OS.


The TCP Fast Open support must also be enabled on the OS level:

  • Linux/macOS: ensure kernel parameter net.ipv4.tcp_fastopen is 2 or 3 for server side, and 1 or 3 for client side.

  • FreeBSD: ensure kernel parameter net.inet.tcp.fastopen.server_enable is 1 for server side, and net.inet.tcp.fastopen.client_enable is 1 for client side.

Default: off


If nonzero, the server will keep up to this number of outgoing TCP connections open for later use. This is an optimization to avoid frequent opening of TCP connections to the same remote.

Change of this parameter requires restart of the Knot server to take effect.

Default: 0


The timeout in seconds after which the unused kept-open outgoing TCP connections to remote servers are closed.

Default: 5


When a connection attempt times out to some remote address, this information will be kept for this specified time (in milliseconds) and other connections to the same address won't be attempted. This prevents repetitive waiting for timeout on an unreachable remote.

Default: 0


If enabled and if SO_REUSEPORT is available on Linux, all configured network sockets are bound to UDP and TCP workers in order to increase the networking performance. This mode isn't recommended for setups where the number of network card queues is lower than the number of UDP or TCP workers.

Change of this parameter requires restart of the Knot server to take effect.

Default: off


A maximum number of TCP clients connected in parallel, set this below the file descriptor limit to avoid resource exhaustion.


It is advisable to adjust the maximum number of open files per process in your operating system configuration.

Default: one half of the file descriptor limit for the server process


Maximum EDNS0 UDP payload size default for both IPv4 and IPv6.

Default: 1232


Maximum EDNS0 UDP payload size for IPv4.

Default: 1232


Maximum EDNS0 UDP payload size for IPv6.

Default: 1232


Enable or disable EDNS Client Subnet support. If enabled, responses to queries containing the EDNS Client Subnet option always contain a valid EDNS Client Subnet option according to RFC 7871.

Default: off


Enable or disable sorted-rrset rotation in the answer section of normal replies. The rotation shift is simply determined by a query ID.

Default: off


One or more IP addresses where the server listens for incoming queries. Optional port specification (default is 53) can be appended to each address using @ separator. Use for all configured IPv4 addresses or :: for all configured IPv6 addresses. Filesystem path can be specified for listening on local unix SOCK_STREAM socket. Non-local address binding is automatically enabled if supported by the operating system.

Change of this parameter requires restart of the Knot server to take effect.

Default: not set

XDP section

Various options related to XDP listening, especially TCP.

    listen: STR[@INT] | ADDR[@INT] ...
    tcp: BOOL
    tcp-max-clients: INT
    tcp-inbuf-max-size: SIZE
    tcp-idle-close-timeout: TIME
    tcp-idle-reset-timeout: TIME
    route-check: BOOL


When you change configuration parameters dynamically or via configuration file reload, some parameters in the XDP section require restarting the Knot server so that the changes take effect.


One or more network device names (e.g. ens786f0) on which the Mode XDP is enabled. Alternatively, an IP address can be used instead of a device name, but the server will still listen on all addresses belonging to the same interface! Optional port specification (default is 53) can be appended to each device name or address using @ separator.

Change of this parameter requires restart of the Knot server to take effect.


If XDP workers only process regular DNS traffic over UDP, it is strongly recommended to also listen on the addresses which are intended to offer the DNS service, at least to fulfil the DNS requirement for working TCP.

Default: not set


If enabled, DNS over TCP traffic is also processed with XDP workers.

The TCP stack features:

  • Basic connection handling, sending/receiving data

  • Close inactive connections

  • Reset inactive connections which aren't able to close

  • Reset invalid connections

  • Ignore invalid resets and ACKs

  • Receive fragmented data – one DNS message in multiple packets

  • Limit total size of incoming buffers, reset most inactive connections with buffered data

  • Send fragmented data – DNS message larger than allowed by MSS

  • Send MSS option calculated from configured MSS and device MTU

  • Receive and honor MSS option, limit the size of outgoing packet

  • Send window size option (set to infinity)

Missing features:

  • Receive and honor window size option, send only such amount of data at once, cache outgoing data

  • Allow multi-message DNS responses (depends on above)

  • Resend lost outgoing packets (not ACKed in time), including data

Change of this parameter requires restart of the Knot server to take effect.


This feature is experimental and it may eat your hamster as well as any other hamsters connected to the network.

Default: off


A maximum number of TCP clients connected in parallel.

Default: 1000000 (one million)


Maximum cumulative size of memory used for buffers of incompletely received messages.

Minimum: 1 MiB

Default: 100 MiB


Time in seconds, after which any idle connection is gracefully closed.

Minimum: 1 s

Default: 10 s


Time in seconds, after which any idle connection is forcibly closed.

Minimum: 1 s

Default: 20 s


If enabled, routing information from the operating system is considered when processing every incoming DNS packet received over the XDP interface:

  • If the outgoing interface of the corresponding DNS response differs from the incoming one, the packet is processed normally by UDP/TCP workers (XDP isn't used).

  • If the destination address is blackholed, unreachable, or prohibited, the DNS packet is dropped without any response.

  • The destination MAC address for the response is taken from the routing system.

If disabled, symmetrical routing is applied. It means that the query source MAC address is used as a response destination MAC address.

Change of this parameter requires restart of the Knot server to take effect.


This mode requires forwarding enabled on the loopback interface (sysctl -w net.ipv4.conf.lo.forwarding=1 and sysctl -w net.ipv6.conf.lo.forwarding=1). If forwarding is disabled, all incoming DNS packets are dropped!

Default: off

Control section

Configuration of the server control interface.

    listen: STR
    timeout: TIME


A UNIX socket path where the server listens for control commands.

Default: rundir/knot.sock


Maximum time (in seconds) the control socket operations can take. Set to 0 for infinity.

Default: 5

Logging section

Server can be configured to log to the standard output, standard error output, syslog (or systemd journal if systemd is enabled) or into an arbitrary file.

There are 6 logging severity levels:

  • critical – Non-recoverable error resulting in server shutdown.

  • error – Recoverable error, action should be taken.

  • warning – Warning that might require user action.

  • notice – Server notice or hint.

  • info – Informational message.

  • debug – Debug or detailed message.

In the case of a missing log section, warning or more serious messages will be logged to both standard error output and syslog. The info and notice messages will be logged to standard output.

  - target: stdout | stderr | syslog | STR
    server: critical | error | warning | notice | info | debug
    control: critical | error | warning | notice | info | debug
    zone: critical | error | warning | notice | info | debug
    any: critical | error | warning | notice | info | debug


A logging output.

Possible values:

  • stdout – Standard output.

  • stderr – Standard error output.

  • syslog – Syslog or systemd journal.

  • file_name – A specific file.

With syslog target, syslog service is used. However, if Knot DNS has been compiled with systemd support and operating system has been booted with systemd, systemd journal is used for logging instead of syslog.


Minimum severity level for messages related to general operation of the server to be logged.

Default: not set


Minimum severity level for messages related to server control to be logged.

Default: not set


Minimum severity level for messages related to zones to be logged.

Default: not set


Minimum severity level for all message types to be logged.

Default: not set

Statistics section

Periodic server statistics dumping.

    timer: TIME
    file: STR
    append: BOOL


A period after which all available statistics metrics will by written to the file.

Default: not set


A file path of statistics output in the YAML format.

Default: rundir/stats.yaml


If enabled, the output will be appended to the file instead of file replacement.

Default: off

Database section

Configuration of databases for zone contents, DNSSEC metadata, or event timers.

    storage: STR
    journal-db: STR
    journal-db-mode: robust | asynchronous
    journal-db-max-size: SIZE
    kasp-db: STR
    kasp-db-max-size: SIZE
    timer-db: STR
    timer-db-max-size: SIZE
    catalog-db: str
    catalog-db-max-size: SIZE


A data directory for storing journal, KASP, and timer databases.

Default: ${localstatedir}/lib/knot (configured with --with-storage=path)


An explicit specification of the persistent journal database directory. Non-absolute path (i.e. not starting with /) is relative to storage.

Default: storage/journal


Specifies journal LMDB backend configuration, which influences performance and durability.

Possible values:

  • robust – The journal database disk synchronization ensures database durability but is generally slower.

  • asynchronous – The journal database disk synchronization is optimized for better performance at the expense of lower database durability in the case of a crash. This mode is recommended on secondary servers with many zones.

Default: robust


The hard limit for the journal database maximum size. There is no cleanup logic in journal to recover from reaching this limit. Journal simply starts refusing changes across all zones. Decreasing this value has no effect if it is lower than the actual database file size.

It is recommended to limit journal-max-usage per-zone instead of journal-db-max-size in most cases. Please keep this value larger than the sum of all zones' journal usage limits. See more details regarding journal behaviour.


This value also influences server's usage of virtual memory.

Default: 20 GiB (512 MiB for 32-bit)


An explicit specification of the KASP database directory. Non-absolute path (i.e. not starting with /) is relative to storage.

Default: storage/keys


The hard limit for the KASP database maximum size.


This value also influences server's usage of virtual memory.

Default: 500 MiB


An explicit specification of the persistent timer database directory. Non-absolute path (i.e. not starting with /) is relative to storage.

Default: storage/timers


The hard limit for the timer database maximum size.


This value also influences server's usage of virtual memory.

Default: 100 MiB


An explicit specification of the zone catalog database directory. Only useful if Catalog zones are enabled. Non-absolute path (i.e. not starting with /) is relative to storage.

Default: storage/catalog


The hard limit for the catalog database maximum size.


This value also influences server's usage of virtual memory.

Default: 20 GiB (512 MiB for 32-bit)

Keystore section

DNSSEC keystore configuration.

  - id: STR
    backend: pem | pkcs11
    config: STR


A keystore identifier.


A key storage backend type.

Possible values:

  • pem – PEM files.

  • pkcs11 – PKCS #11 storage.

Default: pem


A backend specific configuration. A directory with PEM files (the path can be specified as a relative path to kasp-db) or a configuration string for PKCS #11 storage (<pkcs11-url> <module-path>).


Example configuration string for PKCS #11:

"pkcs11:token=knot;pin-value=1234 /usr/lib64/pkcs11/libsofthsm2.so"

Default: kasp-db/keys

Key section

Shared TSIG keys used to authenticate communication with the server.

  - id: DNAME
    algorithm: hmac-md5 | hmac-sha1 | hmac-sha224 | hmac-sha256 | hmac-sha384 | hmac-sha512
    secret: BASE64


A key name identifier.


This value MUST be exactly the same as the name of the TSIG key on the opposite primary/secondary server(s).


A TSIG key algorithm. See TSIG Algorithm Numbers.

Possible values:

  • hmac-md5

  • hmac-sha1

  • hmac-sha224

  • hmac-sha256

  • hmac-sha384

  • hmac-sha512

Default: not set


Shared key secret.

Default: not set

Remote section

Definitions of remote servers for outgoing connections (source of a zone transfer, target for a notification, etc.).

  - id: STR
    address: ADDR[@INT] ...
    via: ADDR[@INT] ...
    key: key_id
    block-notify-after-transfer: BOOL


A remote identifier.


An ordered list of destination IP addresses which are used for communication with the remote server. The addresses are tried in sequence until the remote is reached. Optional destination port (default is 53) can be appended to the address using @ separator.

Default: not set


If the remote is contacted and it refuses to perform requested action, no more addresses will be tried for this remote.


An ordered list of source IP addresses. The first address with the same family as the destination address is used as a source address for communication with the remote. This option can help if the server listens on more addresses. Optional source port (default is random) can be appended to the address using @ separator.

Default: not set


A reference to the TSIG key which is used to authenticate the communication with the remote server.

Default: not set


When incoming AXFR/IXFR from this remote (as a primary server), suppress sending NOTIFY messages to all configured secondary servers.

Default: off

ACL section

Access control list rule definitions. The ACLs are used to match incoming connections to allow or deny requested operation (zone transfer request, DDNS update, etc.).

  - id: STR
    address: ADDR[/INT] | ADDR-ADDR ...
    key: key_id ...
    remote: remote_id ...
    action: notify | transfer | update ...
    deny: BOOL
    update-type: STR ...
    update-owner: key | zone | name
    update-owner-match: sub-or-equal | equal | sub
    update-owner-name: STR ...


An ACL rule identifier.


An ordered list of IP addresses, network subnets, or network ranges. The query's source address must match one of them. Empty value means that address match is not required.

Default: not set


An ordered list of references to TSIG keys. The query must match one of them. Empty value means that transaction authentication is not used.

Default: not set


An ordered list of references to remotes. The query must match one of the remotes. Specifically, one of the remote's addresses and remote's TSIG key if configured must match.


This option cannot be specified along with the address or key option at one ACL item.

Default: not set


An ordered list of allowed (or denied) actions.

Possible values:

  • notify – Allow incoming notify.

  • transfer – Allow zone transfer.

  • update – Allow zone updates.

Default: not set


If enabled, instead of allowing, deny the specified action, address, key, or combination if these items. If no action is specified, deny all actions.

Default: off


A list of allowed types of Resource Records in a zone update. Every record in an update must match one of the specified types.

Default: not set


This option restricts possible owners of Resource Records in a zone update by comparing them to either the TSIG key identity, the current zone name, or to a list of domain names given by the update-owner-name option. The comparison method is given by the update-owner-match option.

Possible values:

  • key — The owner of each updated RR must match the identity of the TSIG key if used.

  • name — The owner of each updated RR must match at least one name in the update-owner-name list.

  • zone — The owner of each updated RR must match the current zone name.

Default: not set


This option defines how the owners of Resource Records in an update are matched to the domain name(s) set by the update-owner option.

Possible values:

  • sub-or-equal — The owner of each Resource Record in an update must either be equal to or be a subdomain of at least one domain set by update-owner.

  • equal — The owner of each updated RR must be equal to at least one domain set by update-owner.

  • sub — The owner of each updated RR must be a subdomain of, but MUST NOT be equal to at least one domain set by update-owner.

Default: sub-or-equal


A list of allowed owners of RRs in a zone update used with update-owner set to name. Every listed owner name which is not FQDN (i.e. it doesn't end in a dot) is considered as if it was appended with the target zone name. Such a relative owner name specification allows better ACL rule reusability across multiple zones.

Default: not set

Submission section

Parameters of KSK submission checks.

  - id: STR
    parent: remote_id ...
    check-interval: TIME
    timeout: TIME


A submission identifier.


A list of references to parent's DNS servers to be checked for presence of corresponding DS records in the case of KSK submission. All of them must have a corresponding DS for the rollover to continue. If none is specified, the rollover must be pushed forward manually.

Default: not set


A DNSSEC-validating resolver can be set as a parent.


Interval for periodic checks of DS presence on parent's DNS servers, in the case of the KSK submission.

Default: 1 hour


After this time period (in seconds) the KSK submission is automatically considered successful, even if all the checks were negative or no parents are configured. Set to 0 for infinity.

Default: 0

Policy section

DNSSEC policy configuration.

  - id: STR
    keystore: keystore_id
    manual: BOOL
    single-type-signing: BOOL
    algorithm: rsasha1 | rsasha1-nsec3-sha1 | rsasha256 | rsasha512 | ecdsap256sha256 | ecdsap384sha384 | ed25519 | ed448
    ksk-size: SIZE
    zsk-size: SIZE
    ksk-shared: BOOL
    dnskey-ttl: TIME
    zone-max-ttl: TIME
    ksk-lifetime: TIME
    zsk-lifetime: TIME
    delete-delay: TIME
    propagation-delay: TIME
    rrsig-lifetime: TIME
    rrsig-refresh: TIME
    rrsig-pre-refresh: TIME
    reproducible-signing: BOOL
    nsec3: BOOL
    nsec3-iterations: INT
    nsec3-opt-out: BOOL
    nsec3-salt-length: INT
    nsec3-salt-lifetime: TIME
    signing-threads: INT
    ksk-submission: submission_id
    ds-push: remote_id
    cds-cdnskey-publish: none | delete-dnssec | rollover | always | double-ds
    cds-digest-type: sha256 | sha384
    offline-ksk: BOOL
    unsafe-operation: none | no-check-keyset | no-update-dnskey | no-update-nsec | no-update-expired ...


A policy identifier.


A reference to a keystore holding private key material for zones.

Default: an imaginary keystore with all default values


A configured keystore called "default" won't be used unless explicitly referenced.


If enabled, automatic key management is not used.

Default: off


If enabled, Single-Type Signing Scheme is used in the automatic key management mode.

Default: off (module onlinesign has default on)


An algorithm of signing keys and issued signatures. See DNSSEC Algorithm Numbers.

Possible values:

  • rsasha1

  • rsasha1-nsec3-sha1

  • rsasha256

  • rsasha512

  • ecdsap256sha256

  • ecdsap384sha384

  • ed25519

  • ed448


Ed25519 algorithm is only available if compiled with GnuTLS 3.6.0+.

Ed448 algorithm is only available if compiled with GnuTLS 3.6.12+ and Nettle 3.6+.

Default: ecdsap256sha256


A length of newly generated KSK or CSK keys.

Default: 2048 (rsa*), 256 (ecdsap256), 384 (ecdsap384), 256 (ed25519), 456 (ed448)


A length of newly generated ZSK keys.

Default: see default for ksk-size


If enabled, all zones with this policy assigned will share one or more KSKs. More KSKs can be shared during a KSK rollover.


As the shared KSK set is bound to the policy id, renaming the policy breaks this connection and new shared KSK set is initiated when a new KSK is needed.

Default: off


A TTL value for DNSKEY records added into zone apex.


Has influence over ZSK key lifetime.


Ensure all DNSKEYs with updated TTL are propagated before any subsequent DNSKEY rollover starts.

Default: zone SOA TTL


Declare (override) maximal TTL value among all the records in zone.


It's generally recommended to override the maximal TTL computation by setting this explicitly whenever possible. It's required for DNSSEC Offline KSK and really reasonable when records are generated dynamically (e.g. by a module).

Default: computed after zone is loaded


A period between KSK activation and the next rollover initiation.


KSK key lifetime is also influenced by propagation-delay, dnskey-ttl, and KSK submission delay.

Zero (aka infinity) value causes no KSK rollover as a result.

This applies for CSK lifetime if single-type-signing is enabled.

Default: 0


A period between ZSK activation and the next rollover initiation.


More exactly, this period is measured since a ZSK is activated, and after this, a new ZSK is generated to replace it within following roll-over.

ZSK key lifetime is also influenced by propagation-delay and dnskey-ttl

Zero (aka infinity) value causes no ZSK rollover as a result.

Default: 30 days


Once a key (KSK or ZSK) is rolled-over and removed from the zone, keep it in the KASP database for at least this period before deleting it completely. This might be useful in some troubleshooting cases when resurrection is needed.

Default: 0


An extra delay added for each key rollover step. This value should be high enough to cover propagation of data from the primary server to all secondary servers.


Has influence over ZSK key lifetime.

Default: 1 hour


A validity period of newly issued signatures.


The RRSIG's signature inception time is set to 90 minutes in the past. This time period is not counted to the signature lifetime.

Default: 14 days


A period how long at least before a signature expiration the signature will be refreshed, in order to prevent expired RRSIGs on secondary servers or resolvers' caches.

Default: 7 days


A period how long at most before a signature refresh time the signature might be refreshed, in order to refresh RRSIGs in bigger batches on a frequently updated zone (avoid re-sign event too often).

Default: 1 hour


For ECDSA algorithms, generate RRSIG signatures deterministically (RFC 6979). Besides better theoretical cryptographic security, this mode allows significant speed-up of loading signed (by the same method) zones. However, the zone signing is a bit slower.

Default: off


Specifies if NSEC3 will be used instead of NSEC.

Default: off


A number of additional times the hashing is performed.

Default: 10


If set, NSEC3 records won't be created for insecure delegations. This speeds up the zone signing and reduces overall zone size.


NSEC3 with the Opt-Out bit set no longer works as a proof of non-existence in this zone.

Default: off


A length of a salt field in octets, which is appended to the original owner name before hashing.

Default: 8


A validity period of newly issued salt field.

Zero value means infinity.

Default: 30 days


When signing zone or update, use this number of threads for parallel signing.

Those are extra threads independent of Background workers.


Some steps of the DNSSEC signing operation are not parallelized.

Default: 1 (no extra threads)


A reference to submission section holding parameters of KSK submission checks.

Default: not set


An optional reference to authoritative DNS server of the parent's zone. The remote server must be configured to accept DS record updates via DDNS. Whenever a CDS record in the local zone is changed, the corresponding DS record is sent as a dynamic update (DDNS) to the parent DNS server. All previous DS records are deleted within the DDNS message. It's possible to manage both child and parent zones by the same Knot DNS server.


This feature requires cds-cdnskey-publish not to be set to none.


Module Onlinesign doesn't support DS push.

Default: not set


Controls if and how shall the CDS and CDNSKEY be published in the zone.

Possible values:

  • none – Never publish any CDS or CDNSKEY records in the zone.

  • delete-dnssec – Publish special CDS and CDNSKEY records indicating turning off DNSSEC.

  • rollover – Publish CDS and CDNSKEY records for ready and not yet active KSK (submission phase of KSK rollover).

  • always – Always publish one CDS and one CDNSKEY records for the current KSK.

  • double-ds – Always publish up to two CDS and two CDNSKEY records for ready and/or active KSKs.


If the zone keys are managed manually, the CDS and CDNSKEY rrsets may contain more records depending on the keys available.

Default: rollover


Specify digest type for published CDS records.

Default: sha256


Specifies if Offline KSK feature is enabled.

Default: off


Turn off some DNSSEC safety features.

Possible values:

  • none – Nothing disabled.

  • no-check-keyset – Don't check active keys in present algorithms. This may lead to violation of RFC 4035#section-2.2.

  • no-update-dnskey – Don't maintain/update DNSKEY, CDNSKEY, and CDS records in the zone apex according to KASP database. Juste leave them as they are in the zone.

  • no-update-nsec – Don't maintain/update NSEC/NSEC3 chain. Leave all the records as they are in the zone.

  • no-update-expired – Don't update expired RRSIGs.

Multiple values may be specified.


This mode is intended for DNSSEC experts who understand the corresponding consequences.

Default: none

Template section

A template is shareable zone settings, which can simplify configuration by reducing duplicates. A special default template (with the default identifier) can be used for global zone configuration or as an implicit configuration if a zone doesn't have another template specified.

  - id: STR
    global-module: STR/STR ...
    # All zone options (excluding 'template' item)


A template identifier.


An ordered list of references to query modules in the form of module_name or module_name/module_id. These modules apply to all queries.


This option is only available in the default template.

Default: not set

Zone section

Definition of zones served by the server.

  - domain: DNAME
    template: template_id
    storage: STR
    file: STR
    master: remote_id ...
    ddns-master: remote_id
    notify: remote_id ...
    acl: acl_id ...
    semantic-checks: BOOL
    zonefile-sync: TIME
    zonefile-load: none | difference | difference-no-serial | whole
    journal-content: none | changes | all
    journal-max-usage: SIZE
    journal-max-depth: INT
    zone-max-size : SIZE
    adjust-threads: INT
    dnssec-signing: BOOL
    dnssec-validation: BOOL
    dnssec-policy: policy_id
    zonemd-verify: BOOL
    zonemd-generate: none | zonemd-sha384 | zonemd-sha512 | remove
    serial-policy: increment | unixtime | dateserial
    refresh-min-interval: TIME
    refresh-max-interval: TIME
    catalog-role: none | interpret | generate | member
    catalog-template: template_id ...
    catalog-zone: DNAME
    catalog-group: STR
    module: STR/STR ...


A zone name identifier.


A reference to a configuration template.

Default: not set or default (if the template exists)


A data directory for storing zone files.

Default: ${localstatedir}/lib/knot (configured with --with-storage=path)


A path to the zone file. Non-absolute path (i.e. not starting with /) is relative to storage. It is also possible to use the following formatters:

  • %c[N] or %c[N-M] – Means the Nth character or a sequence of characters beginning from the Nth and ending with the Mth character of the textual zone name (see %s). The indexes are counted from 0 from the left. All dots (including the terminal one) are considered. If the character is not available, the formatter has no effect.

  • %l[N] – Means the Nth label of the textual zone name (see %s). The index is counted from 0 from the right (0 ~ TLD). If the label is not available, the formatter has no effect.

  • %s – Means the current zone name in the textual representation. The zone name doesn't include the terminating dot (the result for the root zone is the empty string!).

  • %% – Means the % character.


Beware of special characters which are escaped or encoded in the \DDD form where DDD is corresponding decimal ASCII code.

Default: storage/%s.zone


An ordered list of references to zone primary servers (formerly known as master servers).

Default: not set


A reference to zone primary master. If not specified, the first master server is used.

Default: not set


An ordered list of references to remotes to which notify message is sent if the zone changes.

Default: not set


An ordered list of references to ACL rules which can allow or disallow zone transfers, updates or incoming notifies.

Default: not set


If enabled, extra zone semantic checks are turned on.

Several checks are enabled by default and cannot be turned off. An error in mandatory checks causes zone not to be loaded. An error in extra checks is logged only.

Mandatory checks:

  • SOA record missing in the zone (RFC 1034)

  • An extra record together with CNAME record except for RRSIG and DS (RFC 1034)

  • Multiple CNAME record with the same owner

  • DNAME record having a record under it (RFC 2672)

Extra checks:

  • Missing NS record at the zone apex

  • Missing glue A or AAAA record

  • Invalid DNSKEY, DS, or NSEC3PARAM record

  • CDS or CDNSKEY inconsistency

  • Missing, invalid, or unverifiable RRSIG record

  • Invalid NSEC(3) record

  • Broken or non-cyclic NSEC(3) chain

Default: off


The time after which the current zone in memory will be synced with a zone file on the disk (see file). The server will serve the latest zone even after a restart using zone journal, but the zone file on the disk will only be synced after zonefile-sync time has expired (or after manual zone flush). This is applicable when the zone is updated via IXFR, DDNS or automatic DNSSEC signing. In order to completely disable automatic zone file synchronization, set the value to -1. In that case, it is still possible to force a manual zone flush using the -f option.


If you are serving large zones with frequent updates where the immediate sync with a zone file is not desirable, increase the value.

Default: 0 (immediate)


Selects how the zone file contents are applied during zone load.

Possible values:

  • none – The zone file is not used at all.

  • difference – If the zone contents are already available during server start or reload, the difference is computed between them and the contents of the zone file. This difference is then checked for semantic errors and applied to the current zone contents.

  • difference-no-serial – Same as difference, but the SOA serial in the zone file is ignored, the server takes care of incrementing the serial automatically.

  • whole – Zone contents are loaded from the zone file.

When difference is configured and there are no zone contents yet (cold start and no zone contents in the journal), it behaves the same way as whole.

Default: whole


Selects how the journal shall be used to store zone and its changes.

Possible values:

  • none – The journal is not used at all.

  • changes – Zone changes history is stored in journal.

  • all – Zone contents and history is stored in journal.

Default: changes


Policy how much space in journal DB will the zone's journal occupy.


Journal DB may grow far above the sum of journal-max-usage across all zones, because of DB free space fragmentation.

Default: 100 MiB


Maximum history length of the journal.


Zone-in-journal changeset isn't counted to the limit.

Minimum: 2

Default: 2^64


Maximum size of the zone. The size is measured as size of the zone records in wire format without compression. The limit is enforced for incoming zone transfers and dynamic updates.

For incremental transfers (IXFR), the effective limit for the total size of the records in the transfer is twice the configured value. However the final size of the zone must satisfy the configured value.

Default: 2^64


Parallelize internal zone adjusting procedures. This is useful with huge zones with NSEC3. Speedup observable at server startup and while processing NSEC3 re-salt.

Default: 1


If enabled, automatic DNSSEC signing for the zone is turned on.

Default: off


If enabled, the zone contents are validated for being correctly signed (including NSEC/NSEC3 chain) with DNSSEC signatures every time the zone is loaded or changed (including AXFR/IXFR).

When the validation fails, the zone being loaded or update being applied is cancelled with an error, and either none or previous zone state is published.

List of DNSSEC checks:

  • Every zone RRSet is correctly signed by at least one present DNSKEY.

  • DNSKEY RRSet is signed by KSK.

  • NSEC(3) RR exists for each name (unless opt-out) with correct bitmap.

  • Every NSEC(3) RR is linked to the lexicographically next one.

The validation is not affected by dnssec-policy configuration, except for signing-threads option, which specifies the number of threads for parallel validation.


Redundant or garbage NSEC3 records are ignored.

This mode is not compatible with dnssec-signing.


A reference to DNSSEC signing policy.

Default: an imaginary policy with all default values


A configured policy called "default" won't be used unless explicitly referenced.


On each zone load/update, verify that ZONEMD is present in the zone and valid.


Zone digest calculation may take much time and CPU on large zones.

Default: off


On each zone update, calculate ZONEMD and put it into the zone.

Possible values:

  • none – No action regarding ZONEMD.

  • zonemd-sha384 – Generate ZONEMD using SHA384 algorithm.

  • zonemd-sha512 – Generate ZONEMD using SHA512 algorithm.

  • remove – Remove any ZONEMD from the zone apex.

Default: none


Specifies how the zone serial is updated after a dynamic update or automatic DNSSEC signing. If the serial is changed by the dynamic update, no change is made.

Possible values:

  • increment – The serial is incremented according to serial number arithmetic.

  • unixtime – The serial is set to the current unix time.

  • dateserial – The 10-digit serial (YYYYMMDDnn) is incremented, the first 8 digits match the current iso-date.


If the resulting serial for unixtime or dateserial is lower or equal than the current serial (this happens e.g. when migrating from other policy or frequent updates), the serial is incremented instead.

To avoid user confusion, use dateserial only if you expect at most 100 updates per day per zone and unixtime only if you expect at most one update per second per zone.

Default: increment


Forced minimum zone refresh interval to avoid flooding primary server.

Default: 2


Forced maximum zone refresh interval.

Default: not set


Trigger zone catalog feature. Possible values:

  • none – Not a catalog zone.

  • interpret – A catalog zone which is loaded from a zone file or XFR, and member zones shall be configured based on its contents.

  • generate – A catalog zone whose contents are generated according to assigned member zones.

  • member – A member zone that is assigned to one generated catalog zone.

Default: none


For the catalog member zones, the specified configuration template will be applied.

Multiple catalog templates may be defined. The first one is used unless the member zone has the group property defined, matching another catalog template.


This option must be set if and only if catalog-role is interpret.

Default: not set


Assign this member zone to specified generated catalog zone.


This option must be set if and only if catalog-role is member.

The referenced catalog zone must exist and have catalog-role set to generate.

Default: not set


Assign this member zone to specified catalog group (configuration template).


This option has effect if and only if catalog-role is member.

Default: not set


An ordered list of references to query modules in the form of module_name or module_name/module_id. These modules apply only to the current zone queries.

Default: not set


cookies — DNS Cookies

DNS Cookies (RFC 7873) is a lightweight security mechanism against denial-of-service and amplification attacks. The server keeps a secret value (the Server Secret), which is used to generate a cookie, which is sent to the client in the OPT RR. The server then verifies the authenticity of the client by the presence of a correct cookie. Both the server and the client have to support DNS Cookies, otherwise they are not used.


This module introduces two statistics counters:

  • presence – The number of queries containing the COOKIE option.

  • dropped – The number of dropped queries due to the slip limit.


For effective module operation the RRL module must also be enabled and configured after Cookies. See Query modules how to configure modules.


It is recommended to enable DNS Cookies globally, not per zone. The module may be used without any further configuration.

    - id: default
      global-module: mod-cookies # Enable DNS Cookies globally

Module configuration may be supplied if necessary.

  - id: default
    secret-lifetime: 30h # The Server Secret is regenerated every 30 hours
    badcookie-slip: 3    # The server replies only to every third query with a wrong cookie

  - id: default
    global-module: mod-cookies/default # Enable DNS Cookies globally

The value of the Server Secret may also be managed manually using the secret option. In this case the server does not automatically regenerate the Server Secret.

    - id: default
      secret: 0xdeadbeefdeadbeefdeadbeefdeadbeef

Module reference

  - id: STR
    secret-lifetime: TIME
    badcookie-slip: INT
    secret: STR | HEXSTR

A module identifier.


This option configures how often the Server Secret is regenerated. The maximum allowed value is 36 days (RFC 7873#section-7.1).

Default: 26 hours


This option configures how often the server responds to queries containing an invalid cookie by sending them the correct cookie.

  • The value 1 means that the server responds to every query.

  • The value 2 means that the server responds to every second query with an invalid cookie, the rest of the queries is dropped.

  • The value N > 2 means that the server responds to every Nth query with an invalid cookie, the rest of the queries is dropped.

Default: 1


Use this option to set the Server Secret manually. If this option is used, the Server Secret remains the same until changed manually and the secret-lifetime option is ignored. The size of the Server Secret currently MUST BE 16 bytes, or 32 hexadecimal characters.

Default: not set

dnsproxy – Tiny DNS proxy

The module forwards all queries, or all specific zone queries if configured per zone, to the indicated server for resolution. If configured in the fallback mode, only locally unsatisfied queries are forwarded. I.e. a tiny DNS proxy. There are several uses of this feature:

  • A substitute public-facing server in front of the real one

  • Local zones (poor man's "views"), rest is forwarded to the public-facing server

  • Using the fallback to forward queries to a resolver

  • etc.


The module does not alter the query/response as the resolver would, and the original transport protocol is kept as well.


The configuration is straightforward and just a single remote server is required:

  - id: hidden

  - id: default
    remote: hidden
    fallback: on

  - id: default
    global-module: mod-dnsproxy/default

  - domain: local.zone

When clients query for anything in the local.zone, they will be responded to locally. The rest of the requests will be forwarded to the specified server ( in this case).

Module reference

  - id: STR
    remote: remote_id
    timeout: INT
    address: ADDR[/INT] | ADDR-ADDR ...
    fallback: BOOL
    tcp-fastopen: BOOL
    catch-nxdomain: BOOL

A module identifier.


A reference to a remote server where the queries are forwarded to.



A remote response timeout in milliseconds.

Default: 500


An optional list of allowed ranges and/or subnets for query's source address. If the query's address does not fall into any of the configured ranges, the query isn't forwarded.

Default: not set


If enabled, locally unsatisfied queries leading to REFUSED (no zone) are forwarded. If disabled, all queries are directly forwarded without any local attempts to resolve them.

Default: on


If enabled, TCP Fast Open is used when forwarding TCP queries.

Default: off


If enabled, locally unsatisfied queries leading to NXDOMAIN are forwarded. This option is only relevant in the fallback mode.

Default: off

dnstap – Dnstap traffic logging

A module for query and response logging based on the dnstap library. You can capture either all or zone-specific queries and responses; usually you want to do the former.


The configuration comprises only a sink path parameter, which can be either a file or a UNIX socket:

  - id: capture_all
    sink: /tmp/capture.tap

  - id: default
    global-module: mod-dnstap/capture_all


To be able to use a Unix socket you need an external program to create it. Knot DNS connects to it as a client using the libfstrm library. It operates exactly like syslog.


Dnstap log files can also be created or read using kdig.

Module reference

For all queries logging, use this module in the default template. For zone-specific logging, use this module in the proper zone configuration.

  - id: STR
    sink: STR
    identity: STR
    version: STR
    log-queries: BOOL
    log-responses: BOOL
    responses-with-queries: BOOL

A module identifier.


A sink path, which can be either a file or a UNIX socket when prefixed with unix:.



File is overwritten on server startup or reload.


A DNS server identity. Set empty value to disable.

Default: FQDN hostname


A DNS server version. Set empty value to disable.

Default: server version


If enabled, query messages will be logged.

Default: on


If enabled, response messages will be logged.

Default: on


If enabled, dnstap AUTH_RESPONSE messages will also include the original query message as well as the response message sent by the server.

Default: off

geoip — Geography-based responses

This module offers response tailoring based on client's subnet, geographic location, or a statistical weight. It supports GeoIP databases in the MaxMind DB format, such as GeoIP2 or the free version GeoLite2.

The module can be enabled only per zone.


If EDNS Client Subnet support is enabled and if a query contains this option, the module takes advantage of this information to provide a more accurate response.

DNSSEC support

There are several ways to enable DNSSEC signing of tailored responses.

Full zone signing

If automatic DNSSEC signing is enabled, the whole zone is signed by the server and all alternative RRsets, which are responded by the module, are pre-signed when the module is loaded.

This has a speed benefit, however note that every RRset configured in the module should have a default RRset of the same type contained in the zone, so that the NSEC(3) chain can be built correctly. Also, it is STRONGLY RECOMMENDED to use manual key management in this setting, as the corresponding zone has to be reloaded when the signing key changes and to have better control over key synchronization to all instances of the server.


DNSSEC keys for computing record signatures MUST exist in the KASP database or be generated before the module is launched, otherwise the module fails to compute the signatures and does not load.

Module signing

If automatic DNSSEC signing is disabled, it's possible to combine externally pre-signed zone with module pre-signing of the alternative RRsets when the module is loaded. In this mode, only ZSK has to be present in the KASP database. Also in this mode every RRset configured in the module should have a default RRset of the same type contained in the zone.


  - id: presigned_zone
    manual: on
    unsafe-operation: no-check-keyset

  - id: geo_dnssec
    dnssec: on
    policy: presigned_zone

  - domain: example.com.
    module: mod-geoip/geo_dnssec
Online signing

Alternatively, the geoip module may be combined with the onlinesign module and the tailored responses can be signed on the fly. This approach is much more computationally demanding for the server.


If the GeoIP module is used with online signing, it is recommended to set the nsec-bitmap option of the onlinesign module to contain all Resource Record types potentially generated by the module.


An example configuration:

  - id: default
    config-file: /path/to/geo.conf
    ttl: 20
    mode: geodb
    geodb-file: /path/to/GeoLite2-City.mmdb
    geodb-key: [ country/iso_code, city/names/en ]

  - domain: example.com.
    module: mod-geoip/default

Configuration file

Every instance of the module requires an additional config-file in which the desired responses to queries from various locations are configured. This file has the following simple format:

  - geo|net|weight: value1
    RR-Type1: RDATA
    RR-Type2: RDATA
  - geo|net|weight: value2
    RR-Type1: RDATA

Module configuration examples

This section contains some examples for the module's config-file.

Using subnets
  - net:
    A: [, ]
    AAAA: [ 2001:DB8::1, 2001:DB8::2 ]
    TXT: "subnet\"
  - net: 2001:DB8::/32
    AAAA: 2001:DB8::3
    TXT: "subnet\ 2001:DB8::/32"

Clients from the specified subnets will receive the responses defined in the module config. Others will receive the default records defined in the zone (if any).


If a space or a quotation mark is a part of record data, such a character must be prefixed with a backslash. The following notations are equivalent:

Multi-word\ string
"Multi-word\ string"
"\"Multi-word string\""
Using geographic locations
  - geo: "CZ;Prague"
    CNAME: cz.foo.example.com.
  - geo: "US;Las Vegas"
    CNAME: vegas.foo.example.net.
  - geo: "US;*"
    CNAME: us.foo.example.net.

Clients from the specified geographic locations will receive the responses defined in the module config. Others will receive the default records defined in the zone (if any). See geodb-key for the syntax and semantics of the location definitions.

Using weighted records
  - weight: 1
    CNAME: canary.foo.example.com.
  - weight: 10
    CNAME: prod1.foo.example.com.
  - weight: 10
    CNAME: prod2.foo.example.com.

Each response is generated through a random pick where each defined record has a likelihood of its weight over the sum of all weights for the requested name to. Records defined in the zone itself (if any) will never be served.


$ for i in $(seq 1 100); do kdig @ CNAME foo.example.com +short; done | sort | uniq -c
   3 canary.foo.example.com.foo.example.com.
  52 prod1.foo.example.net.foo.example.com.
  45 prod2.foo.example.net.foo.example.com.

Module reference

  - id: STR
    config-file: STR
    ttl: TIME
    mode: geodb | subnet | weighted
    dnssec: BOOL
    policy: policy_id
    geodb-file: STR
    geodb-key: STR ...

A module identifier.


Full path to the response configuration file as described above.



The time to live of Resource Records returned by the module.

Default: 60


The mode of operation of the module.

Possible values:

  • subnet – Responses are tailored according to subnets.

  • geodb – Responses are tailored according to geographic data retrieved from the configured database.

  • weighted – Responses are tailored according to a statistical weight.

Default: subnet


If explicitly enabled, the module signs positive responses based on the module policy (policy). If explicitly disabled, positive responses from the module are not signed even if the zone is pre-signed or signed by the server (dnssec-signing).


This configuration must be used carefully. Otherwise the zone responses can be bogus. DNSKEY rotation isn't supported. So manual mode is highly recommended.

Default: current value of dnssec-signing with dnssec-policy


A reference to DNSSEC signing policy which is used if dnssec is enabled.

Default: an imaginary policy with all default values


Full path to a .mmdb file containing the GeoIP database.

Required if mode is set to geodb


Multi-valued item, can be specified up to 8 times. Each geodb-key specifies a path to a key in a node in the supplied GeoIP database. The module currently supports two types of values: string or 32-bit unsigned int. In the latter case, the key has to be prefixed with (id). Common choices of keys include:

  • continent/code

  • country/iso_code

  • (id)country/geoname_id

  • city/names/en

  • (id)city/geoname_id

  • isp

  • ...

The exact keys available depend on the database being used. To get the full list of keys available, you can e.g. do a sample lookup on your database with the mmdblookup tool.

In the zone's config file for the module the values of the keys are entered in the same order as the keys in the module's configuration, separated by a semicolon. Enter the value "*" if the key is allowed to have any value.

noudp — No UDP response

The module sends empty truncated reply to a query over UDP. Replies over TCP are not affected.


To enable this module for all configured zones and every UDP reply:

  - id: default
    global-module: mod-noudp

Or with specified UDP allow rate:

  - id: sometimes
    udp-allow-rate: 1000  # Don't truncate every 1000th UDP reply

  - id: default
    module: mod-noudp/sometimes

Module reference

 - id: STR
   udp-allow-rate: INT
   udp-truncate-rate: INT


Both udp-allow-rate and udp-truncate-rate cannot be specified together.


Specifies frequency of UDP replies that are not truncated. A non-zero value means that every Nth UDP reply is not truncated.


The rate value is associated with one UDP worker. If more UDP workers are configured, the specified value may not be obvious to clients.

Default: not set


Specifies frequency of UDP replies that are truncated (opposite of udp-allow-rate). A non-zero value means that every Nth UDP reply is truncated.


The rate value is associated with one UDP worker. If more UDP workers are configured, the specified value may not be obvious to clients.

Default: 1

onlinesign — Online DNSSEC signing

The module provides online DNSSEC signing. Instead of pre-computing the zone signatures when the zone is loaded into the server or instead of loading an externally signed zone, the signatures are computed on-the-fly during answering.

The main purpose of the module is to enable authenticated responses with zones which use other dynamic module (e.g., automatic reverse record synthesis) because these zones cannot be pre-signed. However, it can be also used as a simple signing solution for zones with low traffic and also as a protection against zone content enumeration (zone walking).

In order to minimize the number of computed signatures per query, the module produces a bit different responses from the responses that would be sent if the zone was pre-signed. Still, the responses should be perfectly valid for a DNSSEC validating resolver.

Differences from statically signed zones:

  • The NSEC records are constructed as Minimally Covering NSEC Records (RFC 7129#appendix-A). Therefore the generated domain names cover the complete domain name space in the zone's authority.

  • NXDOMAIN responses are promoted to NODATA responses. The module proves that the query type does not exist rather than that the domain name does not exist.

  • Domain names matching a wildcard are expanded. The module pretends and proves that the domain name exists rather than proving a presence of the wildcard.

Records synthesized by the module:

  • DNSKEY record is synthesized in the zone apex and includes public key material for the active signing key.

  • NSEC records are synthesized as needed.

  • RRSIG records are synthesized for authoritative content of the zone.

  • CDNSKEY and CDS records are generated as usual to publish valid Secure Entry Point.


  • Due to limited interaction between the server and the module, after any change to KASP DB (including knotc zone-ksk-submitted command) or when a scheduled DNSSEC event shall be processed (e.g. transition to next DNSKEY rollover state) the server must be reloaded or queried to the zone (with the DO bit set) to apply the change or to trigger the event. For optimal operation, the recommended query frequency is at least ones per second for each zone configured.

  • The NSEC records may differ for one domain name if queried for different types. This is an implementation shortcoming as the dynamic modules cooperate loosely. Possible synthesis of a type by other module cannot be predicted. This dissimilarity should not affect response validation, even with validators performing aggressive negative caching (RFC 8198).


  • Configure the module with an explicit signing policy which has the rrsig-lifetime value in the order of hours.

  • Note that single-type-signing should be set explicitly to avoid fallback to backward-compatible default.


  • Enable the module in the zone configuration with the default signing policy:

      - domain: example.com
        module: mod-onlinesign

    Or with an explicit signing policy:

      - id: rsa
        algorithm: RSASHA256
        ksk-size: 2048
        rrsig-lifetime: 25h
        rrsig-refresh: 20h
      - id: explicit
        policy: rsa
      - domain: example.com
        module: mod-onlinesign/explicit

    Or use manual policy in an analogous manner, see Manual key management.

  • Make sure the zone is not signed and also that the automatic signing is disabled. All is set, you are good to go. Reload (or start) the server:

    $ knotc reload

The following example stacks the online signing with reverse record synthesis module:

  - id: lan-forward
    type: forward
    prefix: ip-
    ttl: 1200

  - domain: corp.example.net
    module: [mod-synthrecord/lan-forward, mod-onlinesign]

Module reference

  - id: STR
    policy: policy_id
    nsec-bitmap: STR ...

A module identifier.


A reference to DNSSEC signing policy. A special default value can be used for the default policy setting.

Default: an imaginary policy with all default values


A list of Resource Record types included in an NSEC bitmap generated by the module. This option should reflect zone contents or synthesized responses by modules, such as synthrecord and GeoIP.

Default: [A, AAAA]

probe — DNS traffic probe

The module allows the server to send simplified information about regular DNS traffic through UNIX sockets. The exported information consists of data blocks where each data block (datagram) describes one query/response pair. The response part can be empty. The receiver can be an arbitrary program using libknot interface (C or Python). In case of high traffic, more channels (sockets) can be configured to allow parallel processing.


Default module configuration:

  - id: default
    global-module: mod-probe

Per zone probe with 8 channels and maximum 1M logs per second limit:

  - id: custom
    prefix: /tmp/knot-probe
    channels: 8
    max-rate: 1000000

  - domain: example.com.
    module: mod-probe/custom

Module reference

  - id: STR
    path: STR
    channels: INT
    max-rate: INT

A module identifier.


A directory path the UNIX sockets are located.


It's recommended to use a directory with the execute permission restricted to the intended probe consumer process owner only.

Default: rundir


Number of channels (UNIX sockets) the traffic is distributed to. In case of high DNS traffic which is beeing processed by many UDP/XDP/TCP workers, using more channels reduces the module overhead.

Default: 1


Maximum number of queries/replies per second the probe is allowed to transfer. If the limit is exceeded, the over-limit traffic is ignored. Zero value means no limit.

Default: 1000

queryacl — Limit queries by remote address or target interface

This module provides a simple way to whitelist incoming queries according to the query's source address or target interface. It can be used e.g. to create a restricted-access subzone with delegations from the corresponding public zone. The module may be enabled both globally and per-zone.


The module limits only regular queries. Notify, transfer and update are handled by ACL.


  - id: default
    address: [,]
    interface: 198.51.100

  - domain: example.com
    module: mod-queryacl/default

Module reference

  - id: STR
    address: ADDR[/INT] | ADDR-ADDR ...
    interface: ADDR[/INT] | ADDR-ADDR ...

A module identifier.


An optional list of allowed ranges and/or subnets for query's source address. If the query's address does not fall into any of the configured ranges, NOTAUTH rcode is returned.

Default: not set


An optional list of allowed ranges and/or subnets for query's target interface. If the interface does not fall into any of the configured ranges, NOTAUTH rcode is returned. Note that every interface used has to be configured in listen.


Don't use values and ::0. These values are redundant and don't work as expected.

Default: not set

rrl — Response rate limiting

Response rate limiting (RRL) is a method to combat DNS reflection amplification attacks. These attacks rely on the fact that source address of a UDP query can be forged, and without a worldwide deployment of BCP38, such a forgery cannot be prevented. An attacker can use a DNS server (or multiple servers) as an amplification source and can flood a victim with a large number of unsolicited DNS responses. The RRL lowers the amplification factor of these attacks by sending some of the responses as truncated or by dropping them altogether.


The module introduces two statistics counters. The number of slipped and dropped responses.


If the Cookies module is active, RRL is not applied for responses with a valid DNS cookie.


You can enable RRL by setting the module globally or per zone.

  - id: default
    rate-limit: 200   # Allow 200 resp/s for each flow
    slip: 2           # Approximately every other response slips

  - id: default
    global-module: mod-rrl/default   # Enable RRL globally

Module reference

  - id: STR
    rate-limit: INT
    slip: INT
    table-size: INT
    whitelist: ADDR[/INT] | ADDR-ADDR ...

A module identifier.


Rate limiting is based on the token bucket scheme. A rate basically represents a number of tokens available each second. Each response is processed and classified (based on several discriminators, e.g. source netblock, query type, zone name, rcode, etc.). Classified responses are then hashed and assigned to a bucket containing number of available tokens, timestamp and metadata. When available tokens are exhausted, response is dropped or sent as truncated (see slip). Number of available tokens is recalculated each second.



Size of the hash table in a number of buckets. The larger the hash table, the lesser the probability of a hash collision, but at the expense of additional memory costs. Each bucket is estimated roughly to 32 bytes. The size should be selected as a reasonably large prime due to better hash function distribution properties. Hash table is internally chained and works well up to a fill rate of 90 %, general rule of thumb is to select a prime near 1.2 * maximum_qps.

Default: 393241


As attacks using DNS/UDP are usually based on a forged source address, an attacker could deny services to the victim's netblock if all responses would be completely blocked. The idea behind SLIP mechanism is to send each Nth response as truncated, thus allowing client to reconnect via TCP for at least some degree of service. It is worth noting, that some responses can't be truncated (e.g. SERVFAIL).

  • Setting the value to 0 will cause that all rate-limited responses will be dropped. The outbound bandwidth and packet rate will be strictly capped by the rate-limit option. All legitimate requestors affected by the limit will face denial of service and will observe excessive timeouts. Therefore this setting is not recommended.

  • Setting the value to 1 will cause that all rate-limited responses will be sent as truncated. The amplification factor of the attack will be reduced, but the outbound data bandwidth won't be lower than the incoming bandwidth. Also the outbound packet rate will be the same as without RRL.

  • Setting the value to 2 will cause that approximately half of the rate-limited responses will be dropped, the other half will be sent as truncated. With this configuration, both outbound bandwidth and packet rate will be lower than the inbound. On the other hand, the dropped responses enlarge the time window for possible cache poisoning attack on the resolver.

  • Setting the value to anything larger than 2 will keep on decreasing the outgoing rate-limited bandwidth, packet rate, and chances to notify legitimate requestors to reconnect using TCP. These attributes are inversely proportional to the configured value. Setting the value high is not advisable.

Default: 1


A list of IP addresses, network subnets, or network ranges to exempt from rate limiting. Empty list means that no incoming connection will be white-listed.

Default: not set

stats — Query statistics

The module extends server statistics with incoming DNS request and corresponding response counters, such as used network protocol, total number of responded bytes, etc (see module reference for full list of supported counters). This module should be configured as the last module.


Server initiated communication (outgoing NOTIFY, incoming *XFR,...) is not counted by this module.


Leading 16-bit message size over TCP is not considered.


Common statistics with default module configuration:

  - id: default
    global-module: mod-stats

Per zone statistics with explicit module configuration:

  - id: custom
    edns-presence: on
    query-type: on

  - id: default
    module: mod-stats/custom

Module reference

  - id: STR
    request-protocol: BOOL
    server-operation: BOOL
    request-bytes: BOOL
    response-bytes: BOOL
    edns-presence: BOOL
    flag-presence: BOOL
    response-code: BOOL
    request-edns-option: BOOL
    response-edns-option: BOOL
    reply-nodata: BOOL
    query-type: BOOL
    query-size: BOOL
    reply-size: BOOL

A module identifier.


If enabled, all incoming requests are counted by the network protocol:

  • udp4 - UDP over IPv4

  • tcp4 - TCP over IPv4

  • udp6 - UDP over IPv6

  • tcp6 - TCP over IPv6

  • udp4-xdp - UDP over IPv4 through XDP

  • tcp4-xdp - TCP over IPv4 through XDP

  • udp6-xdp - UDP over IPv6 through XDP

  • tcp6-xdp - TCP over IPv6 through XDP

Default: on


If enabled, all incoming requests are counted by the server operation. The server operation is based on message header OpCode and message query (meta) type:

  • query - Normal query operation

  • update - Dynamic update operation

  • notify - NOTIFY request operation

  • axfr - Full zone transfer operation

  • ixfr - Incremental zone transfer operation

  • invalid - Invalid server operation

Default: on


If enabled, all incoming request bytes are counted by the server operation:

  • query - Normal query bytes

  • update - Dynamic update bytes

  • other - Other request bytes

Default: on


If enabled, outgoing response bytes are counted by the server operation:

  • reply - Normal response bytes

  • transfer - Zone transfer bytes

  • other - Other response bytes


Dynamic update response bytes are not counted by this module.

Default: on


If enabled, EDNS pseudo section presence is counted by the message direction:

  • request - EDNS present in request

  • response - EDNS present in response

Default: off


If enabled, some message header flags are counted:

  • TC - Truncated Answer in response

  • DO - DNSSEC OK in request

Default: off


If enabled, outgoing response code is counted:


  • ...



  • ...


  • other - All other codes


In the case of multi-message zone transfer response, just one counter is incremented.


Dynamic update response code is not counted by this module.

Default: on


If enabled, EDNS options in requests are counted by their code:

  • CODE0

  • ...


  • other - All other codes

Default: off


If enabled, EDNS options in responses are counted by their code. See request-edns-option.

Default: off


If enabled, NODATA pseudo RCODE (RFC 2308#section-2.2) is counted by the query type:

  • A

  • AAAA

  • other - All other types

Default: off


If enabled, normal query type is counted:

  • A (TYPE1)

  • ...

  • TYPE65

  • SPF (TYPE99)

  • ...

  • TYPE110

  • ANY (TYPE255)

  • ...

  • TYPE260

  • other - All other types


Not all assigned meta types (IXFR, AXFR,...) have their own counters, because such types are not processed as normal query.

Default: off


If enabled, normal query message size distribution is counted by the size range in bytes:

  • 0-15

  • 16-31

  • ...

  • 272-287

  • 288-65535

Default: off


If enabled, normal reply message size distribution is counted by the size range in bytes:

  • 0-15

  • 16-31

  • ...

  • 4080-4095

  • 4096-65535

Default: off

synthrecord – Automatic forward/reverse records

This module is able to synthesize either forward or reverse records for a given prefix and subnet.

Records are synthesized only if the query can't be satisfied from the zone. Both IPv4 and IPv6 are supported.


Automatic forward records
  - id: test1
    type: forward
    prefix: dynamic-
    ttl: 400
    network: 2620:0:b61::/52

  - domain: test.
    file: test.zone # Must exist
    module: mod-synthrecord/test1


$ kdig AAAA dynamic-2620-0-b61-100--1.test.
;; dynamic-2620-0-b61-100--1.test. IN AAAA

dynamic-2620-0-b61-100--1.test. 400 IN AAAA 2620:0:b61:100::1

You can also have CNAME aliases to the dynamic records, which are going to be further resolved:

$ kdig AAAA alias.test.
;; alias.test. IN AAAA

alias.test. 3600 IN CNAME dynamic-2620-0-b61-100--2.test.
dynamic-2620-0-b61-100--2.test. 400 IN AAAA 2620:0:b61:100::2
Automatic reverse records
  - id: test2
    type: reverse
    prefix: dynamic-
    origin: test
    ttl: 400
    network: 2620:0:b61::/52

  - domain: 1.6.b.
    file: 1.6.b. # Must exist
    module: mod-synthrecord/test2


$ kdig -x 2620:0:b61::1

;; ANSWER SECTION: 400 IN PTR dynamic-2620-0-b61--1.test.

Known bugs, limitations

The queries to the empty-non-terminals being parent to synthesized reverse records, e.g. IN PTR with previous example, are answered wrongly NXDOMAIN instead of correct NODATA.

Module reference

  - id: STR
    type: forward | reverse
    prefix: STR
    origin: DNAME
    ttl: INT
    network: ADDR[/INT] | ADDR-ADDR ...
    reverse-short: BOOL

A module identifier.


The type of generated records.

Possible values:

  • forward – Forward records

  • reverse – Reverse records



A record owner prefix.


The value doesn’t allow dots, address parts in the synthetic names are separated with a dash.

Default: empty


A zone origin (only valid for the reverse type).



Time to live of the generated records.

Default: 3600


An IP address, a network subnet, or a network range the query must match.



If enabled, a shortened IPv6 address can be used for reverse record rdata synthesis.

Default: on

whoami — Whoami response

The module synthesizes an A or AAAA record containing the query source IP address, at the apex of the zone being served. It makes sure to allow Knot DNS to generate cacheable negative responses, and to allow fallback to extra records defined in the underlying zone file. The TTL of the synthesized record is copied from the TTL of the SOA record in the zone file.

Because a DNS query for type A or AAAA has nothing to do with whether the query occurs over IPv4 or IPv6, this module requires a special zone configuration to support both address families. For A queries, the underlying zone must have a set of nameservers that only have IPv4 addresses, and for AAAA queries, the underlying zone must have a set of nameservers that only have IPv6 addresses.


To enable this module, you need to add something like the following to the Knot DNS configuration file:

  - domain: whoami.domain.example
    file: "/path/to/whoami.domain.example"
    module: mod-whoami

  - domain: whoami6.domain.example
    file: "/path/to/whoami6.domain.example"
    module: mod-whoami

The whoami.domain.example zone file example:

$TTL 1

@       SOA     (
                        whoami.domain.example.          ; MNAME
                        hostmaster.domain.example.      ; RNAME
                        2016051300                      ; SERIAL
                        86400                           ; REFRESH
                        86400                           ; RETRY
                        86400                           ; EXPIRE
                        1                               ; MINIMUM

$TTL 86400

@       NS      ns1.whoami.domain.example.
@       NS      ns2.whoami.domain.example.
@       NS      ns3.whoami.domain.example.
@       NS      ns4.whoami.domain.example.

ns1     A
ns2     A
ns3     A
ns4     A

The whoami6.domain.example zone file example:

$TTL 1

@       SOA     (
                        whoami6.domain.example.         ; MNAME
                        hostmaster.domain.example.      ; RNAME
                        2016051300                      ; SERIAL
                        86400                           ; REFRESH
                        86400                           ; RETRY
                        86400                           ; EXPIRE
                        1                               ; MINIMUM

$TTL 86400

@       NS      ns1.whoami6.domain.example.
@       NS      ns2.whoami6.domain.example.
@       NS      ns3.whoami6.domain.example.
@       NS      ns4.whoami6.domain.example.

ns1     AAAA    2001:db8:100::53
ns2     AAAA    2001:db8:200::53
ns3     AAAA    2001:db8:300::53
ns4     AAAA    2001:db8:400::53

The parent domain would then delegate whoami.domain.example to ns[1-4].whoami.domain.example and whoami6.domain.example to ns[1-4].whoami6.domain.example, and include the corresponding A-only or AAAA-only glue records.


This module is not configurable.


Knot DNS comes with a few DNS client utilities and a few utilities to control the server. This section collects manual pages for all provided binaries:

knotd – Knot DNS server daemon


knotd [parameters]


Knot DNS is a high-performance authoritative DNS server. The knotd program is the DNS server daemon.

-c, --config file

Use a textual configuration file (default is @config_dir@/knot.conf).

-C, --confdb directory

Use a binary configuration database directory (default is @storage_dir@/confdb). The default configuration database, if exists, has a preference to the default configuration file.

-m, --max-conf-size MiB

Set maximum size of the configuration database (default is @conf_mapsize@ MiB, maximum 10000 MiB).

-s, --socket path

Use a remote control UNIX socket path (default is @run_dir@/knot.sock).

-d, --daemonize [directory]

Run the server as a daemon. New root directory may be specified (default is /).

-v, --verbose

Enable debug output.

-h, --help

Print the program help.

-V, --version

Print the program version.


If the knotd process receives a SIGHUP signal, it reloads its configuration and reopens the log files, if they are configured. Upon receiving a SIGINT signal, knotd exits.

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.

See Also

knot.conf(5), knotc(8), keymgr(8), kjournalprint(8).

knotc – Knot DNS control utility


knotc [parameters] action [action_args]


This program controls a running knotd process using a socket.

If an action is specified, it is performed and knotc exits, otherwise the program is executed in the interactive mode.

-c, --config file

Use a textual configuration file (default is @config_dir@/knot.conf).

-C, --confdb directory

Use a binary configuration database directory (default is @storage_dir@/confdb). The default configuration database, if exists, has a preference to the default configuration file.

-m, --max-conf-size MiB

Set maximum size of the configuration database (default is @conf_mapsize@ MiB, maximum 10000 MiB).

-s, --socket path

Use a control UNIX socket path (default is @run_dir@/knot.sock).

-t, --timeout seconds

Use a control timeout in seconds. Set to 0 for infinity (default is 60). The control socket operations are also subject to the timeout parameter set on the server side in server's Control configuration section.

-b, --blocking

Zone event trigger commands wait until the event is finished. Control timeout is set to infinity if not forced by explicit timeout specification.

-f, --force

Forced operation. Overrides some checks.

-v, --verbose

Enable debug output.

-h, --help

Print the program help.

-V, --version

Print the program version.

status [detail]

Check if the server is running. Details are version for the running server version, workers for the numbers of worker threads, or configure for the configure summary.


Stop the server if running.


Reload the server configuration and modified zone files. All open zone transactions will be aborted!

stats [module[.counter]]

Show global statistics counter(s). To print also counters with value 0, use force option.

zone-status zone [filter]

Show the zone status. Filters are +role, +serial, +transaction, +events, and +freeze.

zone-check [zone...]

Test if the server can load the zone. Semantic checks are executed if enabled in the configuration. If invoked with the force option, an error is returned when semantic check warning appears. (*)

zone-reload [zone...]

Trigger a zone reload from a disk without checking its modification time. For secondary zone, the refresh event from primary server(s) is scheduled; for primary zone, the notify event to secondary server(s) is scheduled. An open zone transaction will be aborted! If invoked with the force option, also zone modules will be re-loaded, but blocking mode might not work reliably. (#)

zone-refresh [zone...]

Trigger a check for the zone serial on the zone's primary server. If the primary server has a newer zone, a transfer is scheduled. This command is valid for secondary zones. (#)

zone-retransfer [zone...]

Trigger a zone transfer from the zone's primary server. The server doesn't check the serial of the primary server's zone. This command is valid for secondary zones. (#)

zone-notify [zone...]

Trigger a NOTIFY message to all configured remotes. This can help in cases when previous NOTIFY had been lost or the secondary servers have been offline. (#)

zone-flush [zone...] [+outdir directory]

Trigger a zone journal flush to the configured zone file. If an output directory is specified, the current zone is immediately dumped (in the blocking mode) to a zone file in the specified directory. See Notes below about the directory permissions. (#)

zone-backup [zone...] +backupdir directory [filter...]

Trigger a zone data and metadata backup to a specified directory. Available filters are +zonefile, +journal, +timers, +kaspdb, +catalog, and their negative counterparts +nozonefile, +nojournal, +notimers, +nokaspdb, and +nocatalog. With these filters set, zone contents, zone's journal, zone related timers, zone related data in the KASP database together with keys, and zone's catalog, respectively, are backed up, or omitted from the backup. By default, filters +zonefile, +timers, +kaspdb, +catalog, and +nojournal are set. Setting a filter for an item doesn't change default settings for other items. If zone flushing is disabled, original zone file is backed up instead of writing out zone contents to a file. See Notes below about the directory permissions. (#)

zone-restore [zone...] +backupdir directory [filter...]

Trigger a zone data and metadata restore from a specified backup directory. Optional filters are equivalent to the same filters of zone-backup. Restore from backups created by Knot DNS releases prior to 3.1 is possible with the force option. See Notes below about the directory permissions. (#)

zone-sign [zone...]

Trigger a DNSSEC re-sign of the zone. Existing signatures will be dropped. This command is valid for zones with DNSSEC signing enabled. (#)

zone-keys-load [zone...]

Trigger a load of DNSSEC keys and other signing material from KASP database (which might have been altered manually). If suitable, re-sign the zone afterwards (keeping valid signatures intact). (#)

zone-key-rollover zone key_type

Trigger immediate key rollover. Publish new key and start a key rollover, even when the key has a lifetime to go. Key type can be ksk (also for CSK) or zsk. This command is valid for zones with DNSSEC signing and automatic key management enabled. Note that complete key rollover consists of several steps and the blocking mode relates to the initial one only! (#)

zone-ksk-submitted zone...

Use when the zone's KSK rollover is in submission phase. By calling this command the user confirms manually that the parent zone contains DS record for the new KSK in submission phase and the old KSK can be retired. (#)

zone-freeze [zone...]

Trigger a zone freeze. All running events will be finished and all new and pending (planned) zone-changing events (load, refresh, update, flush, and DNSSEC signing) will be held up until the zone is thawed. (#)

zone-thaw [zone...]

Trigger dismissal of zone freeze. (#)

zone-read zone [owner [type]]

Get zone data that are currently being presented.

zone-begin zone...

Begin a zone transaction.

zone-commit zone...

Commit the zone transaction. All changes are applied to the zone.

zone-abort zone...

Abort the zone transaction. All changes are discarded.

zone-diff zone

Get zone changes within the transaction.

zone-get zone [owner [type]]

Get zone data within the transaction.

zone-set zone owner [ttl] type rdata

Add zone record within the transaction. The first record in a rrset requires a ttl value specified.

zone-unset zone owner [type [rdata]]

Remove zone data within the transaction.

zone-purge zone... [filter...]

Purge zone data, zone file, journal, timers, and/or KASP data of specified zones. Available filters are +expire, +zonefile, +journal, +timers, and +kaspdb. If no filter is specified, all filters are enabled. If the zone is no longer configured, add +orphan filter (zone file cannot be purged in this case). (#)

zone-stats zone [module[.counter]]

Show zone statistics counter(s). To print also counters with value 0, use force option.


Initialize the configuration database. If the database doesn't exist yet, execute this command as an intended user to ensure the server is permitted to access the database (e.g. sudo -u knot knotc conf-init). (*)


Check the server configuration. (*)

conf-import filename

Import a configuration file into the configuration database. If the database doesn't exist yet, execute this command as an intended user to ensure the server is permitted to access the database (e.g. sudo -u knot knotc conf-import ...). Also ensure the server is not using the configuration database at the same time! (*)

conf-export [filename]

Export the configuration database into a config file or stdout. (*)

conf-list [item]

List the configuration database sections or section items.

conf-read [item]

Read the item from the active configuration database.


Begin a writing configuration database transaction. Only one transaction can be opened at a time.


Commit the configuration database transaction.


Rollback the configuration database transaction.

conf-diff [item]

Get the item difference in the transaction.

conf-get [item]

Get the item data from the transaction.

conf-set item [data...]

Set the item data in the transaction.

conf-unset [item] [data...]

Unset the item data in the transaction.


Empty or -- zone parameter means all zones or all zones with a transaction.

Use @ owner to denote the zone name.

Type item parameter in the form of section[[id]][.name].

(*) indicates a local operation which requires a configuration.

(#) indicates an optionally blocking operation.

The -b and -f options can be placed right after the command name.

Responses returned by knotc commands depend on the mode:

  • In the blocking mode, knotc reports if an error occurred during processing of the command by the server. If an error is reported, a more detailed information about the failure can usually be found in the server log.

  • In the non-blocking (default) mode, knotc doesn't report processing errors. The OK response to triggering commands means that the command has been successfully sent to the server. To verify if the operation succeeded, it's necessary to check the server log.

Actions zone-flush, zone-backup, and zone-restore are carried out by the knotd process. The directory specified must be accessible to the user account that knotd runs under and if the directory already exists, its permissions must be appropriate for that user account.

Interactive mode

The utility provides interactive mode with basic line editing functionality, command completion, and command history.

Interactive mode behavior can be customized in ~/.editrc. Refer to editrc(5) for details.

Command history is saved in ~/.knotc_history.

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.


Reload the whole server configuration
$ knotc reload
Flush the example.com and example.org zones
$ knotc zone-flush example.com example.org
Get the current server configuration
$ knotc conf-read server
Get the list of the current zones
$ knotc conf-read zone.domain
Get the primary servers for the example.com zone
$ knotc conf-read 'zone[example.com].master'
Add example.org zone with a zonefile location
$ knotc conf-begin
$ knotc conf-set 'zone[example.org]'
$ knotc conf-set 'zone[example.org].file' '/var/zones/example.org.zone'
$ knotc conf-commit
Get the SOA record for each configured zone
$ knotc zone-read -- @ SOA

See Also

knotd(8), knot.conf(5), editrc(5).

keymgr – Key management utility


keymgr basic_option [parameters...]

keymgr [config_option config_storage] zone command argument...


The keymgr utility serves for manual key management in Knot DNS server.

Functions for DNSSEC keys and KASP (Key And Signature Policy) management are provided.

The DNSSEC and KASP configuration is stored in a so called KASP database. The database is backed by LMDB.

Basic options
-h, --help

Print the program help.

-V, --version

Print the program version.

-t, --tsig tsig_name [tsig_algorithm] [tsig_bits]

Generates a TSIG key. TSIG algorithm can be specified by string (default: hmac-sha256), bit length of the key by number (default: optimal length given by algorithm). The generated TSIG key is only displayed on stdout: the command does not create a file, nor include the key in a keystore.

-b, --brief

List keys briefly. Output to a terminal is colorized by default.

-l, --list

Print the list of zones that have at least one key stored in the configured KASP database.

-x, --mono

Don't generate colorized output.

-X, --color

Force colorized output in the --brief mode.

Config options
-c, --config file

Use a textual configuration file (default is @config_dir@/knot.conf).

-C, --confdb directory

Use a binary configuration database directory (default is @storage_dir@/confdb). The default configuration database, if exists, has a preference to the default configuration file.

-D, --dir path

Use specified KASP database path and default configuration.


Keymgr runs with the same user privileges as configured for knotd. For example, if keymgr is run as root, but the configured user is knot, it won't be able to read files (PEM files, KASP database, ...) readable only by root.

list [timestamp_format]

Prints the list of key IDs and parameters of keys belonging to the zone.

generate [arguments...]

Generates new DNSSEC key and stores it in KASP database. Prints the key ID. This action takes some number of arguments (see below). Values for unspecified arguments are taken from corresponding policy (if -c or -C options used) or from Knot policy defaults.

import-bind BIND_key_file

Imports a BIND-style key into KASP database (converting it to PEM format). Takes one argument: path to BIND key file (private or public, but both MUST exist).

import-pub BIND_pubkey_file

Imports a public key into KASP database. This key won't be rolled over nor used for signing. Takes one argument: path to BIND public key file.

import-pem PEM_file [arguments...]

Imports a DNSSEC key from PEM file. The key parameters (same as for the generate action) need to be specified (mainly algorithm, timers...) because they are not contained in the PEM format.

import-pkcs11 key_id [arguments...]

Imports a DNSSEC key from PKCS #11 storage. The key parameters (same as for the generate action) need to be specified (mainly algorithm, timers...) because they are not available. In fact, no key data is imported, only KASP database metadata is created.

nsec3-salt [new_salt]

Prints the current NSEC3 salt used for signing. If new_salt is specified, the salt is overwritten. The salt is printed and expected in hexadecimal, or dash if empty.

local-serial [new_serial]

Print SOA serial stored in KASP database when using on-secondary DNSSEC signing. If new_serial is specified, the serial is overwritten. After updating the serial, expire the zone (zone-purge +expire +zonefile +journal) if the server is running, or remove corresponding zone file and journal contents if the server is stopped.

master-serial [new_serial]

Print SOA serial of the remote master stored in KASP database when using on-secondary DNSSEC signing. If new_serial is specified, the serial is overwritten (not recommended).

set key_spec [arguments...]

Changes a timing argument (or ksk/zsk) of an existing key to a new value. Key_spec is either the key tag or a prefix of the key ID, with an optional [id=|keytag=] prefix; arguments are like for generate, but just the related ones.

ds [key_spec]

Generate DS record (all digest algorithms together) for specified key. Key_spec is like for set, if unspecified, all KSKs are used.

dnskey [key_spec]

Generate DNSKEY record for specified key. Key_spec is like for ds, if unspecified, all KSKs are used.

delete key_spec

Remove the specified key from zone. If the key was not shared, it is also deleted from keystore.

share key_ID zone_from

Import a key (specified by full key ID) from another zone as shared. After this, the key is owned by both zones equally.

Generate arguments

Arguments are separated by space, each of them is in format 'name=value'.


Either an algorithm number (e.g. 14), or text name without dashes (e.g. ECDSAP384SHA384).


Key length in bits.


If set to yes, the key will be used for signing DNSKEY rrset. The generated key will also have the Secure Entry Point flag set to 1.


If set to yes, the key will be used for signing zone (except DNSKEY rrset). This flag can be set concurrently with the ksk flag.


Overrides the standard setting of the Secure Entry Point flag.

The following arguments are timestamps of key lifetime (see DNSSEC key states):


Key started to be used for signing, not published (only for algorithm rollover).


Key published.


Key is waiting for submission (only for KSK).


Key used for signing.


Key still used for signing, but another key is active (only for KSK or algorithm rollover).


Key still published, but no longer used for signing.


Key no longer published, but still used for signing (only for algorithm rollover).


Key revoked according to RFC 5011 trust anchor roll-over.


Key deleted.


Zero timestamp means infinite future.


Positive number of seconds since 1970 UTC.


Date and time in this format without any punctuation.


A sign character (+, -), a number, and an optional time unit (y, mo, d, h, mi, s). The default unit is one second. E.g. +1mi, -2mo.

Output timestamp formats

The timestamps are printed as UNIX timestamp.


The timestamps are printed relatively to now using time units (e.g. -2y5mo, +1h13s).


The timestamps are printed in the ISO8601 format (e.g. 2016-12-31T23:59:00).

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.


  1. Generate new TSIG key:

    $ keymgr -t my_name hmac-sha384
  2. Generate new DNSSEC key:

    $ keymgr example.com. generate algorithm=ECDSAP256SHA256 size=256 \
      ksk=true created=1488034625 publish=20170223205611 retire=+10mo remove=+1y
  3. Import a DNSSEC key from BIND:

    $ keymgr example.com. import-bind ~/bind/Kharbinge4d5.+007+63089.key
  4. Configure key timing:

    $ keymgr example.com. set 4208 active=+2mi retire=+4mi remove=+5mi
  5. Share a KSK from another zone:

    $ keymgr example.com. share e687cf927029e9db7184d2ece6d663f5d1e5b0e9 another-zone.com.

See Also

RFC 6781 - DNSSEC Operational Practices. RFC 7583 - DNSSEC Key Rollover Timing Considerations.

knot.conf(5), knotc(8), knotd(8).

kjournalprint – Knot DNS journal print utility


kjournalprint [options] journal_dir zone_name


The program prints zone history stored in a journal database. As default, changes are colored for terminal.

-l, --limit limit

Limits the number of displayed changes.

-s, --serial soa

Start at a specific SOA serial.

-d, --debug

Debug mode brief output.

-z, --zone-list

Instead of reading the journal, display the list of zones in the DB. (zone_name not needed)

-c, --check

Enable additional journal semantic checks during printing.

-x, --mono

Don't generate colorized output.

-n, --no-color

An alias for -x. Use of this option is deprecated, it will be removed in the future.

-X, --color

Force colorized output.

-h, --help

Print the program help.

-V, --version

Print the program version.


A path to the journal database directory.


A name of the zone to print the history for.

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.


Last (most recent) 5 changes without colors:

$ kjournalprint -nl 5 /var/lib/knot/journal example.com.

See Also

knotd(8), knot.conf(5).

kcatalogprint – Knot DNS catalog print utility


kcatalogprint [options] catalog_dir


The program prints zone catalog stored in a catalog database.

-h, --help

Print the program help.

-V, --version

Print the program version.


A path to the catalog database directory (not data.mdb file).

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.

See Also

knotd(8), knot.conf(5).

kzonecheck – Knot DNS zone file checking tool


kzonecheck [options] filename


The utility checks zone file syntax and runs semantic checks on the zone content. The executed checks are the same as the checks run by the Knot DNS server.

Please, refer to the semantic-checks configuration option in knot.conf(5) for the full list of available semantic checks.


Path to the zone file to be checked. For reading from stdin use /dev/stdin or just -.

-o, --origin origin

Zone origin. If not specified, the origin is determined from the file name (possibly removing the .zone suffix).

-d, --dnssec on|off

Also check DNSSEC-related records. The default is to decide based on the existence of a RRSIG for SOA.

-t, --time time

Current time specification. Use UNIX timestamp, YYYYMMDDHHmmSS format, or [+/-]time[unit] format, where unit can be Y, M, D, h, m, or s. Default is current UNIX timestamp.

-v, --verbose

Enable debug output.

-h, --help

Print the program help.

-V, --version

Print the program version.

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.

See Also

knotd(8), knot.conf(5).

kzonesign – DNSSEC signing utility


kzonesign [options] -c conf_file zone_name


This utility reads the zone's zone file, signs the zone according to given configuration, and writes the signed zone file back.

-c, --config conf_file

Knot DNS configuration file (same as for knotd).

-o, --outdir dir_name

Write the output zone file to the specified directory instead of the configured one.

-r, --rollover

Allow key roll-overs and NSEC3 re-salt. In order to finish possible KSK submission, set the KSK's active timestamp to now (+0) using keymgr.

-t, --time timestamp

Sign the zone (and roll the keys if necessary) as if it was at the time specified by timestamp.

-h, --help

Print the program help.

-V, --version

Print the program version.


A name of the zone to be signed.

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.

See Also

knot.conf(5), keymgr(8).

kdig – Advanced DNS lookup utility


kdig [common-settings] [query [settings]]...

kdig -h


This utility sends one or more DNS queries to a nameserver. Each query can have individual settings, or it can be specified globally via common-settings, which must precede query specification.


name | -q name | -x address | -G tapfile

common-settings, settings

[query_class] [query_type] [@server]... [options]


Is a domain name that is to be looked up.


Is a domain name or an IPv4 or IPv6 address of the nameserver to send a query to. An additional port can be specified using address:port ([address]:port for IPv6 address), address@port, or address#port notation. If no server is specified, the servers from /etc/resolv.conf are used.

If no arguments are provided, kdig sends NS query for the root zone.

Query classes

A query_class can be either a DNS class name (IN, CH) or generic class specification CLASSXXXXX where XXXXX is a corresponding decimal class number. The default query class is IN.

Query types

A query_type can be either a DNS resource record type (A, AAAA, NS, SOA, DNSKEY, ANY, etc.) or one of the following:


Generic query type specification where XXXXX is a corresponding decimal type number.


Full zone transfer request.


Incremental zone transfer request for specified SOA serial number (i.e. all zone updates since the specified zone version are to be returned).


Notify message with a SOA serial hint specified.


Notify message with a SOA serial hint unspecified.

The default query type is A.


Use the IPv4 protocol only.


Use the IPv6 protocol only.

-b address

Set the source IP address of the query to address. The address must be a valid address for local interface or :: or An optional port can be specified in the same format as the server value.

-c class

An explicit query_class specification. See possible values above.


Enable debug messages.

-h, --help

Print the program help.

-k keyfile

Use the TSIG key stored in a file keyfile to authenticate the request. The file must contain the key in the same format as accepted by the -y option.

-p port

Set the nameserver port number or service name to send a query to. The default port is 53.

-q name

Set the query name. An explicit variant of name specification. If no name is provided, empty question section is set.

-t type

An explicit query_type specification. See possible values above.

-V, --version

Print the program version.

-x address

Send a reverse (PTR) query for IPv4 or IPv6 address. The correct name, class and type is set automatically.

-y [alg:]name:key

Use the TSIG key named name to authenticate the request. The alg part specifies the algorithm (the default is hmac-sha256) and key specifies the shared secret encoded in Base64.

-E tapfile

Export a dnstap trace of the query and response messages received to the file tapfile.

-G tapfile

Generate message output from a previously saved dnstap file tapfile.


Wrap long records to more lines and improve human readability.


Show record data only.


Use the generic representation format when printing resource record types and data.


Display the DNSSEC keys and signatures values in base64, instead of omitting them.


Set the AA flag.


Set the TC flag.


Set the RD flag.


Same as +[no]rdflag


Set the RA flag.


Set the zero flag bit.


Set the AD flag.


Set the CD flag.


Set the DO flag.


Show all packet sections.


Show the query packet.


Show the packet header.


Show commented section names.


Show the EDNS pseudosection.


Try to show unknown EDNS options as text.


Show the question section.


Show the answer section.


Show the authority section.


Show the additional section.


Show the TSIG pseudosection.


Show trailing packet statistics.


Show the DNS class.


Show the TTL value.


Use the TCP protocol (default is UDP for standard query and TCP for AXFR/IXFR).


Use TCP Fast Open.


Don't use TCP automatically if a truncated reply is received.


Keep TCP connection open for the following query if it has the same connection configuration. This applies to +tcp, +tls, and +https operations. The connection is considered in the context of a single kdig call only.


Use TLS with the Opportunistic privacy profile (RFC 7858#section-4.1).


Use TLS with a certificate validation. Certification authority certificates are loaded from the specified PEM file (default is system certificate storage if no argument is provided). Can be specified multiple times. If the +tls-hostname option is not provided, the name of the target server (if specified) is used for strict authentication.


Use TLS with the Out-of-Band key-pinned privacy profile (RFC 7858#section-4.2). The PIN must be a Base64 encoded SHA-256 hash of the X.509 SubjectPublicKeyInfo. Can be specified multiple times.


Use TLS with a remote server hostname check.


Use TLS with a Server Name Indication.


Use TLS with a client keyfile.


Use TLS with a client certfile.


Use TLS with a valid stapled OCSP response for the server certificate (%u or specify hours). OCSP responses older than the specified period are considered invalid.


Use HTTPS (DNS-over-HTTPS) in wire format (RFC 1035#section-4.2.1). It is also possible to specify URL=[authority][/path] where request will be sent to. Any leading scheme and authority indicator (i.e. //) are ignored. Authority might also be specified as the server (using the parameter @). If path is specified and authority is missing, then the server is used as authority together with the specified path. Library libnghttp2 is required.


Use HTTPS with HTTP/GET method instead of the default HTTP/POST method. Library libnghttp2 is required.


Request the nameserver identifier (NSID).


Set EDNS buffer size in bytes (default is 4096 bytes).


Use EDNS(0) padding option to pad queries, optionally to a specific size. The default is to pad queries with a sensible amount when using +tls, and not to pad at all when queries are sent without TLS. With no argument (i.e., just +padding) pad every query with a sensible amount regardless of the use of TLS. With +nopadding, never pad.


Align the query to B-byte-block message using the EDNS(0) padding option (default is no or 128 if no argument is specified).


Set EDNS(0) client subnet SUBN=addr/prefix.


Use EDNS version (default is 0).


Set the wait-for-reply interval in seconds (default is 5 seconds). This timeout applies to each query attempt. Zero value or notimeout is intepreted as infinity.


Set the number (>=0) of UDP retries (default is 2). This doesn't apply to AXFR/IXFR.


Attach EDNS(0) cookie to the query.


Repeat a query with the correct cookie.


Send custom EDNS option. The CODE is EDNS option code in decimal, HEX is an optional hex encoded string to use as EDNS option value. This argument can be used multiple times. +noednsopt clears all EDNS options specified by +ednsopt.


Disable the IDN transformation to ASCII and vice versa. IDN support depends on libidn availability during project building! If used in common-settings, all IDN transformations are disabled. If used in the individual query settings, transformation from ASCII is disabled on output for the particular query. Note that IDN transformation does not preserve domain name letter case.


Options -k and -y can not be used simultaneously.

Dnssec-keygen keyfile format is not supported. Use keymgr(8) instead.

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.


  1. Get A records for example.com:

    $ kdig example.com A
  2. Perform AXFR for zone example.com from the server

    $ kdig example.com -t AXFR @
  3. Get A records for example.com from and reverse lookup for address 2001:DB8::1 from Both using the TCP protocol:

    $ kdig +tcp example.com -t A @ -x 2001:DB8::1 @
  4. Get SOA record for example.com, use TLS, use system certificates, check for specified hostname, check for certificate pin, and print additional debug info:

    $ kdig -d @ +tls-ca +tls-host=getdnsapi.net \
      +tls-pin=foxZRnIh9gZpWnl+zEiKa0EJ2rdCGroMWm02gaxSc9S= soa example.com
  5. DNS over HTTPS examples (various DoH implementations):

    $ kdig @ +https example.com.
    $ kdig @ +https=/doh example.com.
    $ kdig @ +https +https-get example.com.
    $ kdig @ +https +tls-hostname=dns.google +fastopen example.com.
  6. More queries share one DoT connection:

    $ kdig @ +tls +keepopen abc.example.com A mail.example.com AAAA



See Also

khost(1), knsupdate(1), keymgr(8).

khost – Simple DNS lookup utility


khost [options] name [server]


This utility sends a DNS query for the name to the server and prints a reply in more user-readable form. For more advanced DNS queries use kdig instead.


Is a domain name that is to be looked up. If the name is IPv4 or IPv6 address the PTR query type is used.


Is a name or an address of the nameserver to send a query to. The address can be specified using [address]:port notation. If no server is specified, the servers from /etc/resolv.conf are used.

If no arguments are provided, khost prints a short help.


Use the IPv4 protocol only.


Use the IPv6 protocol only.


Send ANY query with verbose mode.


Enable debug messages.

-h, --help

Print the program help.


Disable recursion.


Use the TCP protocol.


Enable verbose output.

-V, --version

Print the program version.


Wait forever for the reply.

-c class

Set the query class (e.g. CH, CLASS4). The default class is IN.

-t type

Set the query type (e.g. NS, IXFR=12345, TYPE65535). The default is to send 3 queries (A, AAAA and MX).

-R retries

The number (>=0) of UDP retries to query a nameserver. The default is 1.

-W wait

The time to wait for a reply in seconds. This timeout applies to each query try. The default is 2 seconds.

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.


  1. Get the A, AAAA and MX records for example.com:

    $ khost example.com
  2. Get the reverse record for address

    $ khost
  3. Perform a verbose zone transfer for zone example.com:

    $ khost -t AXFR -v example.com



See Also

kdig(1), knsupdate(1).

knsec3hash – NSEC hash computation utility


knsec3hash salt algorithm iterations name


This utility generates a NSEC3 hash for a given domain name and parameters of NSEC3 hash.


Specifies a binary salt encoded as a hexadecimal string.


Specifies a hashing algorithm by number. Currently, the only supported algorithm is SHA-1 (number 1).


Specifies the number of additional iterations of the hashing algorithm.


Specifies the domain name to be hashed.

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.


$ knsec3hash c01dcafe 1 10 knot-dns.cz
7PTVGE7QV67EM61ROS9238P5RAKR2DM7 (salt=c01dcafe, hash=1, iterations=10)
$ knsec3hash - 1 0 net
A1RT98BS5QGC9NFI51S9HCI47ULJG6JH (salt=-, hash=1, iterations=0)

See Also

RFC 5155 – DNS Security (DNSSEC) Hashed Authenticated Denial of Existence.

knotc(8), knotd(8).

knsupdate – Dynamic DNS update utility


knsupdate [options] [filename]


This utility sends Dynamic DNS update messages to a DNS server. Update content is read from a file (if the parameter filename is given) or from the standard input.

The format of updates is textual and is made up of commands. Every command is placed on the separate line of the input. Lines starting with a semicolon are comments and are not processed.


Enable debug messages.

-h, --help

Print the program help.

-k keyfile

Use the TSIG key stored in a file keyfile to authenticate the request. The file should contain the key in the same format, which is accepted by the -y option.

-p port

Set the port to use for connections to the server (if not explicitly specified in the update). The default is 53.

-r retries

The number of retries for UDP requests. The default is 3.

-t timeout

The total timeout (for all UDP update tries) of the update request in seconds. The default is 12. If set to zero, the timeout is infinite.


Use a TCP connection.

-V, --version

Print the program version.

-y [alg:]name:key

Use the TSIG key with a name name to authenticate the request. The alg part specifies the algorithm (the default is hmac-sha256) and key specifies the shared secret encoded in Base64.

server name [port]

Specifies a receiving server of the dynamic update message. The name parameter can be either a host name or an IP address. If the port is not specified, the default port is used. The default port value can be controlled using the -p program option.

local address [port]

Specifies outgoing address and port. If no local is specified, the address and port are set by the system automatically. The default port number is 0.

zone name

Specifies that all updates are done within a zone name. If not specified, the root zone (.) is considered.

origin name

Specifies fully qualified domain name suffix which is appended to non-fqd owners in update commands. The default origin is the root zone.

class name

Sets name as the default class for all updates. If not used, the default class is IN.

ttl value

Sets value as the default TTL (in seconds). If not used, the default value is 0.

key [alg:]name key

Specifies the TSIG key named name to authenticate the request. An optional alg algorithm can be specified. This command has the same effect as the program option -y.

[prereq] nxdomain name

Adds a prerequisite for a non-existing record owned by name.

[prereq] yxdomain name

Adds a prerequisite for an existing record owned by name.

[prereq] nxrrset name [class] type

Adds a prerequisite for a non-existing record of the type owned by name. Internet class is expected.

[prereq] yxrrset name [class] type [data]

Adds a prerequisite for an existing record of the type owned by name with optional data. Internet class is expected.

[update] add name [ttl] [class] type data

Adds a request to add a new resource record into the zone. Please note that if the name is not fully qualified domain name, the current origin name is appended to it.

[update] del[ete] name [ttl] [class] [type] [data]

Adds a request to remove all (or matching class, type or data) resource records from the zone. There is the same requirement for the name parameter as in update add command. The ttl item is ignored.


Displays current content of the update message.


Sends the current update message and cleans the list of updates.


Displays the last answer from the server.


Enable debugging. This command has the same meaning as the -d program option.


Quit the program.


Options -k and -y can not be used simultaneously.

Dnssec-keygen keyfile format is not supported. Use keymgr(8) instead.

Zone name/server guessing is not supported if the zone name/server is not specified.

Empty line doesn't send the update.

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.


  1. Send one update of the zone example.com to the server The update contains two new records:

    $ knsupdate
    > server
    > zone example.com.
    > origin example.com.
    > ttl 3600
    > add test1.example.com. 7200 A
    > add test2 TXT "hello"
    > show
    > send
    > answer
    > quit

See Also

kdig(1), khost(1), keymgr(8).

kxdpgun – DNS benchmarking tool


kxdpgun [options] -i filename targetIP


Powerful generator of DNS traffic, sending and receiving packets through XDP.

Queries are generated according to a textual file which is read sequentially in a loop until a configured duration elapses. The order of queries is not guaranteed. Responses are received (unless disabled) and counted, but not checked against queries.

The number of parallel threads is autodetected according to the number of queues configured for the network interface.

-t, --duration seconds

Duration of traffic generation, specified as a decimal number in seconds (default is 5.0).

-T, --tcp

Send queries over TCP.

-Q, --qps queries

Number of queries-per-second (approximately) to be sent (default is 1000). The program is not optimized for low speeds at which it may lose communication packets. The recommended minimum speed is 2 packets per thread (Rx/Tx queue).

-b, --batch size

Send more queries in a batch. Improves QPS but may affect the counterpart's packet loss (default is 10 for UDP and 1 for TCP).

-r, --drop

Drop incoming responses. Improves QPS, but disables response statistics.

-p, --port number

Remote destination port (default is 53).

-F, --affinity cpu_spec

CPU affinity for all threads specified in the format [<cpu_start>][s<cpu_step>], where <cpu_start> is the CPU ID for the first thread and <cpu_step> is the CPU ID increment for next thread (default is 0s1).

-i, --infile filename

Path to a file with query templates.

-I, --interface interface

Network interface for outgoing communication. This can be useful in situations when the interfaces are in a bond for example.

-l, --local localIP[/prefix]

Override the auto-detected source IP address. If an address range is specified instead, various IPs from the range will be used for different queries uniformly.


The IPv4 or IPv6 address of remote destination.

-h, --help

Print the program help.

-V, --version

Print the program version.

Queries file format

Each line describes a query in the form:

query_name query_type [flags]

Where query_name is a domain name to be queried, query_type is a record type name, and flags is a single character:

E Send query with EDNS.

D Request DNSSEC (EDNS + DO flag).


Sending USR1 signal to a running process triggers current statistics dump to the standard output.


Linux kernel 4.18+ is required.

The utility has to be executed under root or with these capabilities: CAP_NET_RAW, CAP_NET_ADMIN, CAP_SYS_ADMIN, and CAP_SYS_RESOURCE if maximum locked memory limit is too low on Linux < 5.11.

The utility allocates source UDP/TCP ports from the range 2000-65535.

Exit values

Exit status of 0 means successful operation. Any other exit status indicates an error.


Manually created queries file:

abc6.example.com. AAAA
nxdomain.example.com. A
notzone. A
a.example.com. NS E
ab.example.com. A D
abcd.example.com. DS D

Queries file generated from a zone file (Knot DNS format):

cat ZONE_FILE | awk "{print \$1,\$3}" | grep -E "(NS|DS|A|AAAA|PTR|MX|SOA)$" | sort -u -R > queries.txt

Basic usage:

# kxdpgun -i ~/queries.txt 2001:DB8::1

Using UDP with increased batch size:

# kxdpgun -t 20 -Q 1000000 -i ~/queries.txt -b 20 -p 8853

Using TCP:

# kxdpgun -t 20 -Q 100000 -i ~/queries.txt -T -p 8853

See Also



Upgrade 2.4.x to 2.5.x

This chapter describes some steps necessary after upgrading Knot DNS from version 2.4.x to 2.5.x.

Building changes

The --enable-dnstap configure option now enables the dnstap support in kdig only! To build the dnstap query module, --with-module-dnstap have to be used.

Since Knot DNS version 2.5.0 each query module can be configured to be:

  • disabled: --with-module-MODULE_NAME=no

  • embedded: --with-module-MODULE_NAME=yes

  • external: --with-module-MODULE_NAME=shared (excluding dnsproxy and onlinesign)

The --with-timer-mapsize configure option was replaced with the runtime template.max-timer-db-size configuration option.

KASP DB migration

Knot DNS version 2.4.x and earlier uses JSON files to store DNSSEC keys metadata, one for each zone. 2.5.x versions store those in binary format in a LMDB, all zones together. The migration is possible with the pykeymgr script:

$ pykeymgr -i path/to/keydir

The path to KASP DB directory is configuration-dependent, usually it is the keys subdirectory in the zone storage.

In rare installations, the JSON files might be spread across more directories. In such case, it is necessary to put them together into one directory and migrate at once.

Configuration changes

It is no longer possible to configure KASP DB per zone or in a non-default template. Ensure just one common KASP DB configuration in the default template.

As Knot DNS version 2.5.0 brings dynamically loaded modules, some modules were renamed for technical reasons. So it is necessary to rename all occurrences (module section names and references from zones or templates) of the following module names in the configuration:

mod-online-sign -> mod-onlinesign

mod-synth-record -> mod-synthrecord

Upgrade 2.5.x to 2.6.x

Upgrading from Knot DNS version 2.5.x to 2.6.x is almost seamless.

Configuration changes

The dsa and dsa-nsec3-sha1 algorithm values are no longer supported by the algorithm option.

The ixfr-from-differences zone/template option was deprecated in favor of the zonefile-load option.

Upgrade 2.6.x to 2.7.x

Upgrading from Knot DNS version 2.6.x to 2.7.x is seamless if no obsolete configuration or module rosedb is used.

Upgrade 2.7.x to 2.8.x

Upgrading from Knot DNS version 2.7.x to 2.8.x is seamless.

However, if the previous version was migrated (possibly indirectly) from version 2.5.x, the format of the keys stored in Keys And Signature Policy Database is no longer compatible and needs to be updated.

The easiest ways to update how keys are stored in KASP DB is to modify with Keymgr version 2.7.x some of each key's parameters in an undamaging way, e.g.:

$ keymgr example.com. list
$ keymgr example.com. set <keyTag> created=1
$ keymgr example.com. set <keyTag2> created=1

Upgrade 2.8.x to 2.9.x

Upgrading from Knot DNS version 2.8.x to 2.9.x is almost seamless but check the following changes first.

Configuration changes

Miscellaneous changes

Upgrade 2.9.x to 3.0.x

Knot DNS version 3.0.x is functionally compatible with 2.9.x with the following exceptions.


Configuration option update-owner-name is newly FQDN-sensitive. It means that values a.example.com and a.example.com. are not equivalent.

Module synthrecord

Reverse IPv6 address shortening is enabled by default. For example, the module generates:

dynamic-2620-0-b61-100--1.test. 400 IN AAAA 2620:0:b61:100::1

instead of:

dynamic-2620-0000-0b61-0100-0000-0000-0000-0001.test. 400 IN AAAA 2620:0:b61:100::1

Query module API change

The following functions require additional parameter (thread id – qdata->params->thread_id) on the second position:


Building notes

  • The embedded library LMDB is no longer part of the source code. Almost every modern operating system has a sufficient version of this library.

  • DoH support in kdig requires optional library libnghttp2.

  • XDP support on Linux requires optional library libbpf >= 0.0.6. If not available, an embedded library can be used via --enable-xdp=yes configure option.

Upgrade 3.0.x to 3.1.x

Knot DNS version 3.1.x is functionally compatible with 3.0.x with the following exceptions.

Configuration changes

  • Automatic SOA serial incrementation (zonefile-load: difference-no-serial) requires having full zone stored in the journal (journal-content: all). This change is necessary for reliable operation.

  • Replaced options (with backward compatibility):

    Old section

    Old item name

    New section

    New item name





  • Ignored obsolete options (with a notice log):

    • server.max-zone-size

    • server.max-journal-depth

    • server.max-journal-usage

    • server.max-refresh-interval

    • server.min-refresh-interval

    • server.max-ipv4-udp-payload

    • server.max-ipv6-udp-payload

    • server.max-udp-payload

    • server.max-tcp-clients

    • server.tcp-reply-timeout

    • template.journal-db

    • template.kasp-db

    • template.timer-db

    • template.max-journal-db-size

    • template.max-timer-db-size

    • template.max-kasp-db-size

    • template.journal-db-mode

  • Silently ignored obsolete options:

    • server.tcp-handshake-timeout

    • zone.disable-any

Zone backup and restore

The online backup format has changed slightly since 3.0 version. For zone-restore from backups in the previous format, it's necessary to set the -f option. Offline restore procedure of zone files from online backups is different than what it was before. The details are described in Data and metadata backup.

Building notes

  • The configure option --enable-xdp=yes has slightly changed its semantics. It first tries to find an external library libbpf. If it's not detected, the embedded one is used instead.

  • The kxdpgun tool also depends on library libmnl.


Users who use module geoip or dnstap might need installing an additional package with the module.

Knot DNS for BIND users

Automatic DNSSEC signing

Migrating automatically signed zones from BIND to Knot DNS requires copying up-to-date zone files from BIND, importing existing private keys, and updating server configuration:

  1. To obtain current content of the zone which is being migrated, request BIND to flush the zone into the zone file: rndc sync example.com.


    If dynamic updates (DDNS) are enabled for the given zone, you might need to freeze the zone before flushing it. That can be done similarly:

    $ rndc freeze example.com
  2. Copy the fresh zone file into the zones storage directory of Knot DNS.

  3. Import all existing zone keys into the KASP database. Make sure that all the keys were imported correctly:

    $ keymgr example.com. import-bind path/to/Kexample.com.+013+11111
    $ keymgr example.com. import-bind path/to/Kexample.com.+013+22222
    $ ...
    $ keymgr example.com. list


    If the server configuration file or database is not at the default location, add a configuration parameter (-c or -C). See keymgr for more info about required access rights to the key files.

  4. Follow Automatic DNSSEC signing steps to configure DNSSEC signing.


Compatible PKCS #11 Devices

This section has informative character. Knot DNS has been tested with several devices which claim to support PKCS #11 interface. The following table indicates which algorithms and operations have been observed to work. Please notice minimal GnuTLS library version required for particular algorithm support.

Key generate

Key import

ED25519 256-bit

ECDSA 256-bit

ECDSA 384-bit

RSA 1024-bit

RSA 2048-bit

RSA 4096-bit

Feitian ePass 2003









SafeNet Network HSM (Luna SA 4)









SoftHSM 2.0 1









Trustway Proteccio NetHSM


ECDSA only







Ultra Electronics CIS Keyper Plus (Model 9860-2)


RSA only







Utimaco SecurityServer (V4) 2










Algorithms supported depend on support in OpenSSL on which SoftHSM relies. A command similar to the following may be used to verify what algorithms are supported: $ pkcs11-tool --modul /usr/lib64/pkcs11/libsofthsm2.so -M.


Requires setting the number of background workers to 1!

The following table summarizes supported DNSSEC algorithm numbers and minimal GnuTLS library version required. Any algorithm may work with older library, however the supported operations may be limited (e.g. private key import).


GnuTLS version



3.6.0 or newer


13, 14

3.4.8 or newer


5, 7, 8, 10

3.4.6 or newer