Provided by: knot_2.1.1-1build1_amd64 
NAME
knot.conf - Knot DNS configuration file
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 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
There are 8 main sections (server, key, acl, control, remote, template, zone and log) and module sections
with the mod- prefix. The most of the sections (excluding server and control) 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 to specify permanent comment using 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
rate-limit: INT
rate-limit-slip: INT
rate-limit-table-size: INT
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
pidfile
A PID file location.
Default: rundir/knot.pid
udp-workers
A number of quering UDP workers (threads).
Default: auto-estimated optimal value based on the number of online CPUs
tcp-workers
A number of quering TCP workers (threads).
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...). This limit also applies to knotc remote operation over an internet socket.
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
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 rate-limit-slip). Number of available tokens is
recalculated each second.
Default: 0 (disabled)
rate-limit-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
rate-limit-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
max-udp-payload
Maximum EDNS0 UDP payload size.
Default: 4096
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.
algorithm
A key algorithm.
Default: not set
secret
Shared key secret.
Default: not set
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 actions. Empty action list is only allowed if deny is set.
Possible values:
• transfer – Allow zone transfer
• notify – Allow incoming notify
• update – Allow zone updates
Default: not set
deny
Deny if address, key and action match.
Default: off
CONTROL SECTION
Configuration of the server control interface.
control:
listen: STR
listen
A UNIX socket path where the server listens for remote control commands.
Default: rundir/knot.sock
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
key
A reference to the TSIG key which ise used to autenticate the communication with the remote server.
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
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.
Caution: This option is only available in the default template.
Default: storage/timers
global-module
An ordered list of references to query modules in the form module_name/module_id. These modules apply to
all queries.
Caution: 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
file: STR
storage: 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-size: SIZE
dnssec-signing: BOOL
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)
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. 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
storage
A data directory for storing zone files, journal files and timers database.
Default: ${localstatedir}/lib/knot (configured with --with-storage=path)
master
An ordered list of references to zone master servers.
Default: not set
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)
• CNAME link chain length greater than 10 (including infinite cycles)
• DNAME and CNAME records under the same owner (RFC 2672)
• CNAME and DNAME wildcards pointing to themselves
• 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
• Extra record types under the same name as NSEC3 record (this is RFC-valid, but Knot will not serve such
a zone correctly)
• NSEC3-unsecured 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
• Not all RRs in the node are signed
• 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).
Caution: 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)
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.
Caution: This option has no effect with enabled dnssec-signing.
Default: off
max-journal-size
Maximum size of the zone journal file.
Default: 2^64
dnssec-signing
If enabled, automatic DNSSEC signing for the zone is turned on.
Caution: Cannot be enabled on a slave zone.
Default: off
kasp-db
A KASP database path. Non absolute path is relative to storage.
Default: storage/keys
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 arithmetic
• unixtime – The serial is set to the current unix time
Caution: 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 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 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 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
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
• file_name – File
server
Minimum severity level for messages related to general operation of the server that are logged.
Default: not set
zone
Minimum severity level for messages related to zones that are logged.
Default: not set
any
Minimum severity level for all message types that are logged.
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
id
A module identifier.
sink
A sink path, which can be either a file or a UNIX socket when prefixed with unix:.
Required
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 records
• reverse – Reverse records
Required
prefix
A record owner prefix.
Caution: prefix 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
MODULE DNSPROXY
The module catches all unsatisfied queries and forwards them to the indicated server for resolution.
mod-dnsproxy:
- id: STR
remote: remote_id
catch-nxdomain: BOOL
id
A module identifier.
remote
A reference to a remote server where the queries are forwarded to.
Required
catch-nxdomain
If enabled, all unsatisfied queries (also applies to local zone lookups) are forwarded.
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.
dbdir
A path to the directory where the database is stored.
Required
MODULE ONLINE-SIGN
The module provides online DNSSEC signing.
mod-online-sign:
- id: STR
id
A module identifier.
AUTHOR
CZ.NIC Labs <http://www.knot-dns.cz>
COPYRIGHT
Copyright 2010–2016, CZ.NIC, z.s.p.o.
2.1.1 2016-02-10 KNOT.CONF(5)