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
The configuration consists of several fixed sections and optional module
sections. There are 14 fixed sections (module, server, 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: [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 a 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
Module section¶
Dynamic modules loading configuration.
Note
If configured with non-empty `--with-moduledir=path` parameter, all
shared modules in this directory will be automatically loaded.
module:
- id: STR
file: STR
id¶
A module identifier in the form of the mod- prefix and module name suffix.
file¶
A path to a shared library file with the module implementation.
Warning
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.
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
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] ...
listen-xdp: STR[@INT] | ADDR[@INT] ...
Caution
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.
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 (RFC 4892).
Set to an 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 (RFC 4892). Set to an empty value to disable.
Default: server version
nsid¶
A DNS name server identifier (RFC 5001). Set to an empty value to disable.
Default: FQDN hostname
rundir¶
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)
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.
Change of this parameter requires restart of the Knot server to take effect.
Default: root:root
pidfile¶
A PID file location.
Change of this parameter requires restart of the Knot server to take effect.
Default: rundir/knot.pid
udp-workers¶
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
tcp-workers¶
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
background-workers¶
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
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-idle-timeout¶
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
tcp-io-timeout¶
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
Caution
In order to reduce the risk of Slow Loris attacks, it’s recommended setting this limit as low as possible on public servers.
tcp-remote-io-timeout¶
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
tcp-reuseport¶
If enabled, each TCP worker listens on its own socket and the OS kernel socket load balancing is emloyed 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
socket-affinity¶
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
tcp-max-clients¶
A maximum number of TCP clients connected in parallel, set this below the file descriptor limit to avoid resource exhaustion.
Note
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
edns-client-subnet¶
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
answer-rotation¶
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
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. 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
listen-xdp¶
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.
Default: not set
Caution
Since 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.
Control section¶
Configuration of the server control interface.
control:
listen: STR
timeout: TIME
timeout¶
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.
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 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.
server¶
Minimum severity level for messages related to general operation of the server to be logged.
Default: not set
control¶
Minimum severity level for messages related to server control to be logged.
Default: not set
Statistics section¶
Periodic server statistics dumping.
statistics:
timer: TIME
file: STR
append: BOOL
Database section¶
Configuration of databases for zone contents, DNSSEC metadata, or event timers.
database:
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
storage¶
A data directory for storing journal, KASP, and timer databases.
Default: ${localstatedir}/lib/knot (configured with --with-storage=path)
journal-db¶
An explicit specification of the persistent journal database directory.
Non-absolute path (i.e. not starting with /) is relative to
storage.
Default: storage/journal
journal-db-mode¶
Specifies journal LMDB backend configuration, which influences performance and durability.
Possible values:
robust– The journal database disk sychronization 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
journal-db-max-size¶
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.
Note
This value also influences server’s usage of virtual memory.
Default: 20 GiB (512 MiB for 32-bit)
kasp-db¶
An explicit specification of the KASP database directory.
Non-absolute path (i.e. not starting with /) is relative to
storage.
Default: storage/keys
kasp-db-max-size¶
The hard limit for the KASP database maximum size.
Note
This value also influences server’s usage of virtual memory.
Default: 500 MiB
timer-db¶
An explicit specification of the persistent timer database directory.
Non-absolute path (i.e. not starting with /) is relative to
storage.
Default: storage/timers
timer-db-max-size¶
The hard limit for the timer database maximum size.
Note
This value also influences server’s usage of virtual memory.
Default: 100 MiB
catalog-db¶
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
catalog-db-max-size¶
The hard limit for the catalog database maximum size.
Note
This value also influences server’s usage of virtual memory.
Default: 20 GiB (512 MiB for 32-bit)
Keystore section¶
DNSSEC keystore configuration.
keystore:
- id: STR
backend: pem | pkcs11
config: STR
id¶
A keystore identifier.
backend¶
A key storage backend type.
Possible values:
pem– PEM files.pkcs11– PKCS #11 storage.
Default: pem
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 (<pkcs11-url> <module-path>).
Note
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.
key:
- id: DNAME
algorithm: hmac-md5 | hmac-sha1 | hmac-sha224 | hmac-sha256 | hmac-sha384 | hmac-sha512
secret: BASE64
id¶
A key name identifier.
Note
This value MUST be exactly the same as the name of the TSIG key on the opposite primary/secondary server(s).
algorithm¶
A TSIG key algorithm. See TSIG Algorithm Numbers.
Possible values:
hmac-md5hmac-sha1hmac-sha224hmac-sha256hmac-sha384hmac-sha512
Default: not set
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
block-notify-after-transfer: BOOL
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 until the
remote is reached. Optional destination port (default is 53)
can be appended to the address using @ separator.
Default: not set
Note
If the remote is contacted and it refuses to perform requested action, no more addresses will be tried for this remote.
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
key¶
A reference to the TSIG key which is used to authenticate the communication with the remote server.
Default: not set
block-notify-after-transfer¶
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.).
acl:
- 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 ...
id¶
An ACL rule identifier.
address¶
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
key¶
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
remote¶
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.
Default: not set
action¶
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
deny¶
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
update-type¶
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
update-owner¶
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
update-owner-match¶
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
update-owner-name¶
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.
submission:
- id: STR
parent: remote_id ...
check-interval: TIME
timeout: TIME
id¶
A submission identifier.
parent¶
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
Tip
A DNSSEC-validating resolver can be set as a parent.
check-interval¶
Interval for periodic checks of DS presence on parent’s DNS servers, in the case of the KSK submission.
Default: 1 hour
timeout¶
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.
policy:
- id: STR
keystore: STR
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
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
offline-ksk: BOOL