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Manual Reference Pages  -  GDNSD.ZONEFILE (5)

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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 and $ORIGIN 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.

$ADDR_LIMIT_V4 is a non-standard, gdnsd-specific directive. It requires a single unsigned integer argument. The argument limits the total number of A records to include in the server’s responses for any given A rrset (whether static or dynamic). The default limit is zero, which is interpreted as no limit. Setting the limit via this directive affects all rrsets until the value is changed again by another directive. gdnsd always rotates the RRs of an address RR-set in a round-robin fashion, and this rotation occurs before the limit is applied, allowing a small pseudo-random subset of a larger list to be delivered via this mechanism.

$ADDR_LIMIT_V6 same as above, but for IPv6 AAAA rrsets.

The RFC-standard $INCLUDE directive is not supported because it would greatly complicate the detection of zone update transactions with our current filesystem-based change detection scheme. Most legitimate uses of $INCLUDE to reduce redundancy should be replaced with a zonefile-generating script instead, perhaps using a template system.

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.


gdnsd(8) supports the following standard RR types with their standard RDATA formats: SOA, A, AAAA, NS, PTR, CNAME, MX, SRV, TXT, and NAPTR. All RRs must be in class IN, which is the implicit default.

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. Note however that gdnsd does not allow using the RFC 3597 format for types gdnsd explicitly supports (all of which predate 3597 anyways), and that even in the RFC 3597 case we still only allow class IN RRs.

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. This includes not only direct responses to A and AAAA queries, but also things like Additional-section RRs and ANY-query output. DYNA cannot co-exist with actual static A or AAAA records at the same name, but can co-exist with any other RR-type.


  ; 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. While DYNC responses are included in ANY queries for the given name, they are not used in Additional-section processing, even when the plugin responds with address records rather than CNAME.


  ; asks plugin geoip to provide address data or a CNAME
  ;  (at the plugins 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).


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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gdnsd 2.2.2 GDNSD.ZONEFILE (5) 2016-04-03

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