Ubuntu Manpage: gdnsd.zonefile - gdnsd zonefile syntax

NAME

       gdnsd.zonefile - gdnsd zonefile syntax

SYNOPSIS

       example.com:

         $TTL 86400

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

         @     NS      ns1.example.com.
         @     NS      ns2
         @     NS      ns.example.net.

         ns1   A       192.0.2.1 ; a comment
         ns2.example.com.      A       192.0.2.2

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

         $ttl 86400
         ; a comment
         mail-a        A 192.0.2.3
         mail-b        A 192.0.2.4

         subz          NS      ns1.subz
         subz          NS      ns2.subz
         ns1.subz      A       192.0.2.5
         ns2.subz      A       192.0.2.6

         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 ..."

DESCRIPTION

       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.

DIRECTIVES

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.

SUPPORTED RESOURCE RECORD TYPES

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

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 traditional standard RR types, but it
can be used to encode data for the non-traditional types.

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

DYNA
"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.

Example:

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

DYNC
"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".

Example:

; 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/DYNC TTLs
"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.

Examples:

; 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).

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