Brandon Black edited this page Feb 16, 2019 · 6 revisions


gdnsd.zonefile - gdnsd zonefile syntax


$TTL 86400

@       SOA ns1 hostmaster (
      1      ; serial
      7200   ; refresh
      30M    ; retry
      3D     ; expire
      900    ; ncache

@       NS
@       NS      ns2
@       NS

ns1     A ; a comment        A

@       7200    MX      10 mail-a
@       7200    MX      100 mail-b

$ttl 86400
; a comment
mail-a  A
mail-b  A

subz            NS      ns1.subz
subz            NS      ns2.subz
ns1.subz        A
ns2.subz        A

www     600/10  DYNA    some_plugin!resource_name
alias           CNAME   www

_http._tcp      1800    SRV     5 500 80 www

foo             TXT     "blah blah" "blah"
_spf            TXT     "v=spf1 ..."


This is the primary zonefile syntax for gdnsd(8). The syntax is designed to be as close as possible to the standard zonefile syntax from RFC 1035 (which is the "standard" format one typically sees with traditional BIND servers). This document will just cover a few important highlights and/or deviations from the norm.


The standard $TTL, $ORIGIN, and $INCLUDE directives are supported with their normal syntax and semantics:

$TTL changes the default TTL of any records coming after it, and can occur multiple times. Note that in the absence of a zonefile-level $TTL setting, the default TTL comes from the global config option zones_default_ttl, which in turn defaults to 86400 (1 day).

$ORIGIN changes what is appended to unqualified hostnames (those lacking a final .) seen in the zone file from that point forward, as well as any @ entries (which is an alias for the current origin). $ORIGIN itself may also be an unqualified name, in which case the previous origin is appended to it. Any fully-qualified $ORIGIN must be within the zone described by this zonefile. The default origin is the zone name itself.

$INCLUDE includes another file as if its contents existed at the point of the $INCLUDE directive. Include directives may specify an optional origin, which has the same effect as $ORIGIN at the top of the included file. Changes to the origin (and default ttl) within included files have no effect on the outer file.

BIND's $GENERATE extension is not supported at this time, but there's no fundamental reason it couldn't be added at a later date.


The standard @, as a whole name, is supported as an alias for the current origin. In addition to this, gdnsd implements two special extensions @Z and @F. These denote the current zone name, and the original origin (before any internal $ORIGIN declarations) of the file currently being parsed. Unlike @, they can also be used as the final label of an unqualified name. @Z and @F will always be equivalent to each other in the main zonefile for a zone, but may differ when parsing included files from "$INCLUDE". As an example:

* zones/ has the line "$INCLUDE includes/foo foo"
* zones/includes/foo has these lines:
   $ORIGIN bar
   asdf A
   $ORIGIN baz.@F
   asdf A
   $ORIGIN quux.@Z
   asdf A
* This results in creating all of these: A A    A

Note that the origin changes accomplished with @F and @Z backtrack towards the root of the name hierarchy, and thus wouldn't normally be possible without explicitly using the zone name itself. The main benefit of these directives is they allow this kind of origin-switching behavior while keeping all zone data relative to the zone name rather than absolute. When combined with the fact that the zones scanner will load symlinks, this means the above zones/ could also be symlinked as zones/, loading all the same files and providing an identical tree of data under the other zone name without conflict.


All RRs must be of class IN, which is the implicit default.

gdnsd(8) supports the following standard RR types with their standard RDATA formats:

traditional: SOA, A, AAAA, NS, PTR, CNAME, MX, SRV, TXT, NAPTR non-traditional: CAA explicitly unsupported: HINFO

It also supports the generic format for unknown RR types documented in RFC 3597, which has syntax like:

foo TYPE31337 \# 10 0123456789 ABCDEF0123

... which indicates an RR of numeric type 31337 containing 10 bytes of RDATA, specified as the final part of the RR as a pair of 5-byte hex strings. See RFC 3597 itself for full details.

gdnsd does not allow using the RFC3597 format to specify any of the supported traditional standard RR types, but it can be used to encode data for the non-traditional types. It's also not allowed to use RFC3597 to specify HINFO RRs, as these are now reserved in gdnsd for use in handling ANY queries, using the RFC 8482 HINFO option.

SOA records' negative-caching TTL is set to the minimum of the traditional "minimum" (last) field (which always means "negative cache TTL" as of RFC 2308), and the actual TTL of the SOA record itself. This TTL is used as the actual TTL of the SOA record any time it is emitted, whether for negative or positive answers.

Additionally, gdnsd supports two special-case, non-standard virtual resource record types DYNA and DYNC:


DYNA is for dynamically-determined address records (both A and AAAA) via plugin code. The right-hand-side of a DYNA RR is a plugin name and a resource name separated by an exclamation mark. The named plugin will be fed the resource name and the DNS client's IP address and/or edns-client-subnet information, and it is up to the plugin code which addresses of which types to return in the response.

The dynamic plugin lookup for DYNA will be used anywhere that regular A and/or AAAA records would be used. DYNA cannot co-exist with actual static A or AAAA records at the same name, but can co-exist with any other RR-type.

DYNA and DYNAAAA RRs cannot be used to supply the addresses of nameservers. In other words, any name that exists in zone scope on the right-hand-side of an NS record cannot have DYNA or DYNAAAA (and relatedly, must have at least one of A or AAAA).


; asks plugin 'geoip' to provide address data from
;  its resource named 'pubwww' for address queries.
foo DYNA geoip!pubwww
foo MX 10 mail


DYNC has the same syntax as DYNA above, but different data rules. Plugins results returned via DYNC can be either addresses or a CNAME record. DYNC cannot co-exist with any other resource record at the same name, much like normal CNAME RRs. This also implies that DYNC cannot be used at the zone root, as the zone root requires NS and SOA RRs.

DYNC's dynamic CNAME targets cannot be used to point at names in the same zonefile as the DYNC record; they must be used to point at other zones.


; asks plugin 'geoip' to provide address data or a CNAME
;  (at the plugin's discretion) for its resource named
;  'www'.  No other RRs of any type for name 'foo' are
;  legal alongside this record.
foo DYNC geoip!www


DYNA and DYNC TTL fields have a syntax extension and slightly different meanings than the TTL field of a traditional, fixed RR. The format for DYNA/DYNC TTLs is MAX[/MIN], with MIN defaulting to half of MAX if not specified explicitly.

Based on the configuration and state of the underlying monitored services, (see "service_types" in gdnsd.config(8)), gdnsd knows the minimum time to the next possible state-change which could affect a given DYNA or DYNC result. For example, given the configuration and state, it may be known that in order for a currently DOWN address to transition to the UP state (and thus change the answer to a given query) would require 7 more successful monitoring checks in a row at 8-second intervals, and therefore cannot happen in less than 56 seconds. In this case 56 seconds would be the internally-calculated TTL.

In cases where multiple monitored resources factor into a plugin's decision and/or response (e.g. multifo), the calculated TTL will generally be the minimum of all involved internal monitoring TTLs. This calculated TTL is then clamped to the MAX and MIN limits from the zonefile.


; Explicit range of 30 - 300:
www 300/30 DYNC weighted!foo
; Implicit range of 150 - 300:
www 300 DYNA metafo!myservice
; Avoid all TTL-mangling and use a fixed value of 10 minutes:
www 600/600 DYNA geoip!foo-dist

TXT data auto-splitting

gdnsd's TXT RRs support the auto-splitting of long string constants. Rather than manually breaking the data into 255-byte chunks as required by the protocol, you can specify a single long chunk and have the server break it at 255 byte boundaries automatically. (this behavior can be disabled via gdnsd.config(5) as well, which will turn oversized chunks into zonefile parsing errors).

TXT records are limited to a maximum of 16000 bytes when encoded in rdata form for wire transmission.


gdnsd(8), gdnsd.config(5)

The gdnsd manual.


Copyright (c) 2012 Brandon L Black <>

This file is part of gdnsd.

gdnsd is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

gdnsd is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with gdnsd. If not, see <>.

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