Configuration Reference¶
Description¶
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
0xprefix) - BOOL – Boolean value (
on/offortrue/false) - TIME – Number of seconds, an integer with possible time multiplier suffix (
s~ 1,m~ 60,h~ 3600 ord~ 24 * 3600) - SIZE – Number of bytes, an integer with possible size multiplier suffix (
B~ 1,K~ 1024,M~ 1024^2 orG~ 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
There are 11 main sections (server, control, log, statistics, keystore, policy, key, acl, remote, template, and zone) and module sections with the mod- prefix. Most of the sections (excluding server, control, and statistics) are sequences of settings blocks. Each settings block begins with a unique identifier, which can be used as a reference from other sections (such identifier must be defined in advance).
A multi-valued item can be specified either as a YAML sequence:
address: [10.0.0.1, 10.0.0.2]
or as more single-valued items each on an extra line:
address: 10.0.0.1
address: 10.0.0.2
If an item value contains spaces or other special characters, it is necessary to enclose such value within double quotes " ".
Comments¶
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.
Includes¶
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
Server section¶
General options related to the server.
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-handshake-timeout: TIME
tcp-idle-timeout: TIME
tcp-reply-timeout: TIME
max-tcp-clients: INT
max-udp-payload: SIZE
max-ipv4-udp-payload: SIZE
max-ipv6-udp-payload: SIZE
listen: ADDR[@INT] ...
identity¶
An identity of the server returned in the response to the query for TXT record id.server. or hostname.bind. in the CHAOS class (see RFC 4892). Set empty value to disable.
Default: FQDN hostname
version¶
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 (see RFC 4892). Set empty value to disable.
Default: server version
nsid¶
A DNS name server identifier (see RFC 5001). Set empty value to disable.
Default: FQDN hostname
rundir¶
A path for storing run-time data (PID file, unix sockets, etc.).
Default: ${localstatedir}/run/knot (configured with --with-rundir=path)
user¶
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.
Default: root:root
udp-workers¶
A number of UDP workers (threads) used to process incoming queries over UDP.
Default: auto-estimated optimal value based on the number of online CPUs
tcp-workers¶
A number of TCP workers (threads) used to process incoming queries over TCP.
Default: auto-estimated optimal value based on the number of online CPUs
background-workers¶
A number of workers (threads) used to execute background operations (zone loading, zone updates, etc.).
Default: auto-estimated optimal value based on the number of online CPUs
async-start¶
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
tcp-handshake-timeout¶
Maximum time between newly accepted TCP connection and the first query. This is useful to disconnect inactive connections faster than connections that already made at least 1 meaningful query.
Default: 5
tcp-idle-timeout¶
Maximum idle time between requests on a TCP connection. This also limits receiving of a single query, each query must be received in this time limit.
Default: 20
tcp-reply-timeout¶
Maximum time to wait for an outgoing connection or for a reply to an issued request (SOA, NOTIFY, AXFR...).
Default: 10
max-tcp-clients¶
A maximum number of TCP clients connected in parallel, set this below the file descriptor limit to avoid resource exhaustion.
Default: 100
listen¶
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 0.0.0.0 for all configured IPv4 addresses or :: for all configured IPv6 addresses.
Default: not set
Key section¶
Shared TSIG keys used to authenticate communication with the server.
key:
- id: DNAME
algorithm: hmac-md5 | hmac-sha1 | hmac-sha224 | hmac-sha256 | hmac-sha384 | hmac-sha512
secret: BASE64
id¶
A key name identifier.
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.).
acl:
- id: STR
address: ADDR[/INT] | ADDR-ADDR ...
key: key_id ...
action: notify | transfer | update ...
deny: BOOL
id¶
An ACL rule identifier.
address¶
An ordered list of IP addresses, network subnets, or network ranges. The query must match one of them. Empty value means that address match is not required.
Default: not set
key¶
An ordered list of references to TSIG keys. The query must match one of them. Empty value means that TSIG key is not required.
Default: not set
action¶
An ordered list of allowed (or denied) actions.
Possible values:
transfer– Allow zone transfernotify– Allow incoming notifyupdate– Allow zone updates
Default: not set
Statistics section¶
Periodic server statistics dumping.
statistics:
timer: TIME
file: STR
append: BOOL
Keystore section¶
DNSSEC keystore configuration.
keystore:
- id: STR
backend: pem | pkcs11
config: STR
id¶
A keystore identifier.
config¶
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.
Note
Example configuration string for PKCS #11:
"pkcs11:token=knot;pin-value=1234 /usr/lib64/pkcs11/libsofthsm2.so"
Default: kasp-db/keys
Policy section¶
DNSSEC policy configuration.
policy:
- id: STR
keystore: STR
manual: BOOL
single-type-signing: BOOL
algorithm: dsa | rsasha1 | dsa-nsec3-sha1 | rsasha1-nsec3-sha1 | rsasha256 | rsasha512 | ecdsap256sha256 | ecdsap384sha384
ksk-size: SIZE
zsk-size: SIZE
dnskey-ttl: TIME
zsk-lifetime: TIME
propagation-delay: TIME
rrsig-lifetime: TIME
rrsig-refresh: TIME
nsec3: BOOL
nsec3-iterations: INT
nsec3-salt-length: INT
nsec3-salt-lifetime: TIME
id¶
A policy identifier.
keystore¶
A reference to a keystore holding private key material for zones. A special default value can be used for the default keystore settings.
Default: default
single-type-signing¶
If enabled, Single-Type Signing Scheme is used in the automatic key management mode.
Note
Because key rollover is not supported yet, just one combined signing key is generated if none is available.
Default: off
ksk-size¶
A length of newly generated KSK keys.
Default: 1024 (dsa*), 2048 (rsa*), 256 (ecdsap256*), 384 (ecdsap384*)
dnskey-ttl¶
A TTL value for DNSKEY records added into zone apex.
Default: zone SOA TTL
Note
has infuence over ZSK key lifetime
zsk-lifetime¶
A period between ZSK publication and the next rollover initiation.
Default: 30 days
Note
ZSK key lifetime is also infuenced by propagation-delay and dnskey-ttl
propagation-delay¶
An extra delay added for each key rollover step. This value should be high enough to cover propagation of data from the master server to all slaves.
Default: 1 day
Note
has infuence over ZSK key lifetime
rrsig-refresh¶
A period how long before a signature expiration the signature will be refreshed.
Default: 7 days
nsec3-salt-length¶
A length of a salt field in octets, which is appended to the original owner name before hashing.
Default: 8
Remote section¶
Definitions of remote servers for outgoing connections (source of a zone transfer, target for a notification, etc.).
remote:
- id: STR
address: ADDR[@INT] ...
via: ADDR[@INT] ...
key: key_id
id¶
A remote identifier.
address¶
An ordered list of destination IP addresses which are used for communication with the remote server. The addresses are tried in sequence unless the operation is successful. Optional destination port (default is 53) can be appended to the address using @ separator.
Default: not set
via¶
An ordered list of source IP addresses. The first address with the same family as the destination address is used. Optional source port (default is random) can be appended to the address using @ separator.
Default: not set
Template section¶
A template is a shareable zone setting which can be used for configuration of many zones in one place. A special default template (with the default identifier) can be used for global querying configuration or as an implicit configuration if a zone doesn't have another template specified.
template:
- id: STR
timer-db: STR
journal-db: STR
journal-db-mode: robust | asynchronous
max-journal-db-size: SIZE
global-module: STR/STR ...
# All zone options (excluding 'template' item)
id¶
A template identifier.
timer-db¶
Specifies a path of the persistent timer database. The path can be specified as a relative path to the default template storage.
Note
This option is only available in the default template.
Default: storage/timers
journal-db¶
Specifies a path of the persistent journal database. The path can be specified as a relative path to the default template storage.
Note
This option is only available in the default template.
Default: storage/journal
journal-db-mode¶
Specifies journal LMDB backend configuration, which influences performance and durability.
Possible values:
robust– The journal DB disk sychronization ensures DB durability but is generally slowerasynchronous– The journal DB disk synchronization is optimized for better perfomance at the expense of lower DB durability; this mode is recommended only on slave nodes with many zones
Note
This option is only available in the default template.
Default: robust
max-journal-db-size¶
Hard limit for the common journal DB. 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 lower than actual DB file size.
It is recommended to limit max-journal-usage per-zone instead of max-journal-size in most cases. Please keep this value large enough. This value also influences server's usage of virtual memory.
Note
This option is only available in the default template.
Default: 20 GiB
global-module¶
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.
Note
This option is only available in the default template.
Default: not set
Zone section¶
Definition of zones served by the server.
zone:
- 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
disable-any: BOOL
zonefile-sync: TIME
ixfr-from-differences: BOOL
max-journal-usage: SIZE
max-journal-depth: INT
max-zone-size : SIZE
dnssec-signing: BOOL
dnssec-policy: STR
kasp-db: STR
request-edns-option: INT:[HEXSTR]
serial-policy: increment | unixtime
module: STR/STR ...
domain¶
A zone name identifier.
template¶
A reference to a configuration template.
Default: not set or default (if the template exists)
storage¶
A data directory for storing zone files, journal files and timers database.
Default: ${localstatedir}/lib/knot (configured with --with-storage=path)
file¶
A path to the zone file. Non absolute path 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 (beware of special characters which are escaped or encoded in the \DDD form where DDD is corresponding decimal ASCII code). The zone name doesn't include the terminating dot (the result for the root zone is the empty string!).%%– means the%character
Default: storage/%s.zone
ddns-master¶
A reference to zone primary master server. If not specified, the first master server is used.
Default: not set
notify¶
An ordered list of references to remotes to which notify message is sent if the zone changes.
Default: not set
acl¶
An ordered list of references to ACL rules which can allow or disallow zone transfers, updates or incoming notifies.
Default: not set
semantic-checks¶
If enabled, extra zone file 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:
- An extra record together with CNAME record (except for RRSIG and DS)
- SOA record missing in the zone (RFC 1034)
- DNAME records having records under it (DNAME children) (RFC 2672)
Extra checks:
- Missing NS record at the zone apex
- Missing glue A or AAAA records
- Broken or non-cyclic NSEC(3) chain
- Wrong NSEC(3) type bitmap
- Multiple NSEC records at the same node
- Missing NSEC records at authoritative nodes
- NSEC3 insecure delegation that is not part of Opt-out span
- Wrong original TTL value in NSEC3 records
- Wrong RDATA TTL value in RRSIG record
- Signer name in RRSIG RR not the same as in DNSKEY
- Signed RRSIG
- Wrong key flags or wrong key in RRSIG record (not the same as ZSK)
Default: off
disable-any¶
If enabled, all authoritative ANY queries sent over UDP will be answered with an empty response and with the TC bit set. Use this option to minimize the risk of DNS reflection attack.
Default: off
zonefile-sync¶
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 disable automatic zonefile synchronization, -1 value can be used (manual zone flush is still possible).
Note
If you are serving large zones with frequent updates where the immediate sync with a zone file is not desirable, increase the value.
Warning
If the zone file is not up-to-date, the zone should be flushed before its zone file editation or the SOA record must be untouched after editation. Otherwise the journal can't be applied.
Default: 0 (immediate)
ixfr-from-differences¶
If enabled, the server creates zone differences from changes you made to the zone file upon server reload. This option is relevant only if the server is a master server for the zone.
Note
This option has no effect with enabled dnssec-signing.
Default: off
max-journal-usage¶
Policy how much space in journal DB will the zone's journal occupy.
Default: 100 MiB
Note
Journal DB may grow far above the sum of max-journal-usage across all zones, because of DB free space fragmentation.
max-zone-size¶
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
dnssec-signing¶
If enabled, automatic DNSSEC signing for the zone is turned on.
Note
Cannot be enabled on a slave zone.
Default: off
dnssec-policy¶
A reference to DNSSEC signing policy. A special default value can be used for the default policy settings.
Required
request-edns-option¶
An arbitrary EDNS0 option which is included into a server request (AXFR, IXFR, SOA, or NOTIFY). The value is in the option_code:option_data format.
Default: not set
serial-policy¶
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 arithmeticunixtime– The serial is set to the current unix time
Note
If your serial was in other than unix time format, be careful with the transition to unix time. It may happen that the new serial will be 'lower' than the old one. If this is the case, the transition should be done by hand (see RFC 1982).
Default: increment
module¶
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
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 shutdownerror– Recoverable error, action should be takenwarning– Warning that might require user actionnotice– Server notice or hintinfo– Informational messagedebug– Debug messages (must be turned on at compile time)
In the case of 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.
log:
- 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
target¶
A logging output.
Possible values:
stdout– Standard outputstderr– Standard error outputsyslog– Syslog- file_name – File
server¶
Minimum severity level for messages related to general operation of the server that are logged.
Default: not set
control¶
Minimum severity level for messages related to server control that are logged.
Default: not set
Module rrl¶
A response rate limiting module.
mod-rrl:
- id: STR
rate-limit: INT
slip: INT
table-size: INT
whitelist: ADDR[/INT] | ADDR-ADDR ...
id¶
A module identifier.
rate-limit¶
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.
Required
table-size¶
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
slip¶
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 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
whitelist¶
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
Module dnstap¶
The module dnstap allows query and response logging.
For all queries logging, use this module in the default template. For zone-specific logging, use this module in the proper zone configuration.
mod-dnstap:
- id: STR
sink: STR
identity: STR
version: STR
log-queries: BOOL
log-responses: BOOL
id¶
A module identifier.
Module online-sign¶
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.
mod-online-sign:
- id: STR
policy: STR
id¶
A module identifier.
Module synth-record¶
This module is able to synthesize either forward or reverse records for the given prefix and subnet.
mod-synth-record:
- id: STR
type: forward | reverse
prefix: STR
origin: DNAME
ttl: INT
network: ADDR[/INT] | ADDR-ADDR
id¶
A module identifier.
type¶
The type of generated records.
Possible values:
forward– Forward recordsreverse– Reverse records
Required
prefix¶
A record owner prefix.
Note
The value doesn’t allow dots, address parts in the synthetic names are separated with a dash.
Default: empty
Module dnsproxy¶
The module catches all unsatisfied queries and forwards them to the indicated server for resolution.
mod-dnsproxy:
- id: STR
remote: remote_id
timeout: INT
fallback: BOOL
catch-nxdomain: BOOL
id¶
A module identifier.
fallback¶
If enabled, localy 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
catch-nxdomain¶
If enabled, localy unsatisfied queries leading to NXDOMAIN are forwarded. This option is only relevant in the fallback mode.
Default: off
Module rosedb¶
The module provides a mean to override responses for certain queries before the available zones are searched for the record.
mod-rosedb:
- id: STR
dbdir: STR
id¶
A module identifier.
Module stats¶
The module provides incoming query processing statistics.
Note
Leading 16-bit message size over TCP is not considered.
mod-stats:
- id: STR
request-protocol: BOOL
server-operation: BOOL
request-bytes: BOOL
response-bytes: BOOL
edns-presence: BOOL
flag-presence: BOOL
response-code: BOOL
reply-nodata: BOOL
query-type: BOOL
query-size: BOOL
reply-size: BOOL
id¶
A module identifier.
request-protocol¶
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
Default: on
server-operation¶
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
request-bytes¶
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
response-bytes¶
If enabled, outgoing response bytes are counted by the server operation:
- reply - Normal response bytes
- transfer - Zone transfer bytes
- other - Other response bytes
Warning
Dynamic update response bytes are not counted by this module.
Default: on
edns-presence¶
If enabled, EDNS pseudo section presence is counted by the message direction:
- request - EDNS present in request
- response - EDNS present in response
Default: off
flag-presence¶
If enabled, some message header flags are counted:
- TC - Truncated Answer in response
- DO - DNSSEC OK in request
Default: off
response-code¶
If enabled, outgoing response code is counted:
- NOERROR
- ...
- NOTZONE
- BADVERS
- ...
- BADCOOKIE
- other - All other codes
Note
In the case of multi-message zone transfer response, just one counter is incremented.
Warning
Dynamic update response code is not counted by this module.
Default: on
reply-nodata¶
If enabled, NODATA pseudo RCODE (see RFC 2308, Section 2.2) is counted by the query type:
- A
- AAAA
- other - All other types
Default: off
query-type¶
If enabled, normal query type is counted:
- A (TYPE1)
- ...
- TYPE65
- SPF (TYPE99)
- ...
- TYPE110
- ANY (TYPE255)
- ...
- TYPE260
- other - All other types
Note
Not all assigned meta types (IXFR, AXFR,...) have their own counters, because such types are not processed as normal query.
Default: off
query-size¶
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
reply-size¶
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
