Modules

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.

Note

This module introduces a statistics counter: the number of queries containing the COOKIE option.

Warning

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

Example

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

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

Module configuration may be supplied if necessary.

mod-cookies:
  - 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

template:
  - 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.

mod-cookies:
    - id: default
      secret: 0xdeadbeefdeadbeefdeadbeefdeadbeef

Module reference

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

id

A module identifier.

secret-lifetime

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

badcookie-slip

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

secret

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 localy 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.

Note

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

Example

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

remote:
  - id: hidden
    address: 10.0.1.1

mod-dnsproxy:
  - id: default
    remote: hidden
    fallback: on

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

zone:
  - 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 (10.0.1.1 in this case).

Module reference

mod-dnsproxy:
  - id: STR
    remote: remote_id
    timeout: INT
    fallback: BOOL
    catch-nxdomain: BOOL

id

A module identifier.

remote

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

Required

timeout

A remote response timeout in milliseconds.

Default: 500

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

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.

Example

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

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

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

Note

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.

Note

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.

mod-dnstap:
  - id: STR
    sink: STR
    identity: STR
    version: STR
    log-queries: BOOL
    log-responses: BOOL

id

A module identifier.

sink

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

Required

Warning

File is overwritten on server startup or reload.

identity

A DNS server identity. Set empty value to disable.

Default: FQDN hostname

version

A DNS server version. Set empty value to disable.

Default: server version

log-queries

If enabled, query messages will be logged.

Default: on

log-responses

If enabled, response messages will be logged.

Default: on

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.

Note

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.

Note

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.

Example:

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

mod-geoip:
  - id: geo_dnssec
    ...
    dnssec: on
    policy: presigned_zone

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.

Note

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.

Example

An example configuration:

mod-geoip:
  - 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 ]

zone:
  - 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:

domain-name1:
  - geo|net|weight: value1
    RR-Type1: RDATA
    RR-Type2: RDATA
    ...
  - geo|net|weight: value2
    RR-Type1: RDATA
  ...
domain-name2:
...

Module configuration examples

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

Using subnets

foo.example.com:
  - net: 10.0.0.0/24
    A: [ 192.168.1.1, 192.168.1.2 ]
    AAAA: [ 2001:DB8::1, 2001:DB8::2 ]
    TXT: "subnet\ 10.0.0.0/24"
  ...
bar.example.com:
  - net: 2001:DB8::/32
    A: 192.168.1.3
    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).

Note

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

foo.example.com:
  - 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

foo.example.com:
  - 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 likelyhood 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.

Result:

$ for i in $(seq 1 100); do kdig @192.168.1.242 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

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

id

A module identifier.

config-file

Full path to the response configuration file as described above.

Required

ttl

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

Default: 60

mode

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

dnssec

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).

Warning

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

policy

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

Default: an imaginary policy with all default values

geodb-file

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

Required if mode is set to geodb

geodb-key

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.

Example

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

template:
  - id: default
    global-module: mod-noudp

Or with specified UDP allow rate:

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

template:
  - id: default
    module: mod-noudp/sometimes

Module reference

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

Note

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

udp-allow-rate

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

Note

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

udp-truncate-rate

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.

Note

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.

Limitations:

  • 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).

Recommendations:

  • 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.

Example

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

    zone:
      - domain: example.com
        module: mod-onlinesign
    

    Or with an explicit signing policy:

    policy:
      - id: rsa
        algorithm: RSASHA256
        ksk-size: 2048
        rrsig-lifetime: 25h
        rrsig-refresh: 20h
    
    mod-onlinesign:
      - id: explicit
        policy: rsa
    
    zone:
      - 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:

mod-synthrecord:
  - id: lan-forward
    type: forward
    prefix: ip-
    ttl: 1200
    network: 192.168.100.0/24

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

Module reference

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

id

A module identifier.

policy

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

nsec-bitmap

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.

Example

Default module configuration:

template:
  - id: default
    global-module: mod-probe

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

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

zone:
  - domain: example.com.
    module: mod-stats/custom

Module reference

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

id

A module identifier.

path

A directory path the UNIX sockets are located.

Note

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

Default: rundir

channels

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

max-rate

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.

Note

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

Example

mod-queryacl:
  - id: default
    address: [192.0.2.73-192.0.2.90, 203.0.113.0/24]
    interface: 198.51.100

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

Module reference

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

id

A module identifier.

address

A 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.

interface

A 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.

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.

Note

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

Note

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

Example

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

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

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

Module reference

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 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

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

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.

Note

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

Note

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

Example

Common statistics with default module configuration:

template:
  - id: default
    global-module: mod-stats

Per zone statistics with explicit module configuration:

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

template:
  - id: default
    module: mod-stats/custom

Module reference

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
    request-edns-option: BOOL
    response-edns-option: 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
  • udp4-xdp - UDP over IPv4 through XDP
  • udp6-xdp - UDP over IPv6 through XDP

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

request-edns-option

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

  • CODE0
  • EDNS-KEY-TAG (CODE14)
  • other - All other codes

Default: off

response-edns-option

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

Default: off

reply-nodata

If enabled, NODATA pseudo RCODE (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

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.

Example

Automatic forward records

mod-synthrecord:
  - id: test1
    type: forward
    prefix: dynamic-
    ttl: 400
    network: 2620:0:b61::/52

zone:
  - domain: test.
    file: test.zone # Must exist
    module: mod-synthrecord/test1

Result:

$ kdig AAAA dynamic-2620-0-b61-100--1.test.
...
;; QUESTION SECTION:
;; dynamic-2620-0-b61-100--1.test. IN AAAA

;; ANSWER SECTION:
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.
...
;; QUESTION SECTION:
;; alias.test. IN AAAA

;; ANSWER SECTION:
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

mod-synthrecord:
  - id: test2
    type: reverse
    prefix: dynamic-
    origin: test
    ttl: 400
    network: 2620:0:b61::/52

zone:
  - domain: 1.6.b.0.0.0.0.0.0.2.6.2.ip6.arpa.
    file: 1.6.b.0.0.0.0.0.0.2.6.2.ip6.arpa.zone # Must exist
    module: mod-synthrecord/test2

Result:

$ kdig -x 2620:0:b61::1
...
;; QUESTION SECTION:
;; 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.6.b.0.0.0.0.0.0.2.6.2.ip6.arpa. IN PTR

;; ANSWER SECTION:
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.6.b.0.0.0.0.0.0.2.6.2.ip6.arpa. 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. 0.0.0.0.1.6.b.0.0.0.0.0.0.2.6.2.ip6.arpa. IN PTR with previous example, are answered wrongly NXDOMAIN instead of correct NODATA.

Module reference

mod-synthrecord:
  - id: STR
    type: forward | reverse
    prefix: STR
    origin: DNAME
    ttl: INT
    network: ADDR[/INT] | ADDR-ADDR ...
    reverse-short: BOOL

id

A module identifier.

type

The type of generated records.

Possible values:

  • forward – Forward records
  • reverse – 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

origin

A zone origin (only valid for the reverse type).

Required

ttl

Time to live of the generated records.

Default: 3600

network

An IP address, a network subnet, or a network range the query must match.

Required

reverse-short

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.

Example

To enable this module, you need to add something like the following to the Knot DNS configuration file:

zone:
  - domain: whoami.domain.example
    file: "/path/to/whoami.domain.example"
    module: mod-whoami

zone:
  - 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       198.51.100.53
ns2     A       192.0.2.53
ns3     A       203.0.113.53
ns4     A       198.19.123.53

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.

Note

This module is not configurable.