#!/bin/bash
# Copyright (c) 2002, 2003, 2004 Mark Suter <suter@humbug.org.au>
#
# This shell script uses utilities shipped with ISC BIND to
# update a zone using Dynamic DNS Update requests (RFC2136).
#
# This program 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 2 of the License, or
# (at your option) any later version.
#
# This program 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.
#
# $Id: dynamic-dns-update,v 1.2 2004/06/19 11:49:32 suter Exp $

################################
##  Start User Configuration  ##
################################

## The interface who's address we want published
internet=ppp0

## The Time To Live we should use
ttl=$(( 60 * 30 ))

## The hostname we're doing dynamic updates on
hostname=host.example.org

## IP address of DNS server to update
dnsserver=192.0.2.1

## Version of local nsupdate utility (nine or eight)
version=nine

## Bind v9 nsupdate:
keyname=$hostname		## Whatever the server expects
key="TG6KQ9zBEzvGcsWKRO96zA=="  ## Shared key (no files needed)

## Bind v8 nsupdate:
keydir=/etc/named/tsig          ## Dir with *.key and *.private files (no trailing slash!)

## With v8 nsupdate, $dnsserver is ignored - nsupdate queries the DNS,
## thus requiring a valid delegation.

################################
##   Bind v9 Documentation    ##
################################

# This key was generated using bind9's dnssec-keygen(8) utility,
# for example,
#
#    $ dnssec-keygen -a HMAC-MD5 -b 128 -n host host.example.org
#    $ cat Khost.example.org.*.key
#    host.example.org. IN KEY 512 3 157 TG6KQ9zBEzvGcsWKRO96zA==
#
# Here's a corresponding configuration for ISC BIND 9:
#
#     key "host.example.org" {
#         algorithm hmac-md5;
#         secret "wJrOTT0umFTIllqV1Xk8sQ==";
#     };
#
#     zone "example.org" {
#         ...
#         update-policy { grant * self - A; };
#     };
#
# More information is available in the Administrator Reference Manual
# shipped with BIND 9 and available from http://www.isc.org/sw/bind/

################################
##   Bind v8 Documentation    ##
################################

## If possible, please use bind v9.

# The key files needed may be generated using bind8's dnskeygen(8)
# utility, for example,
#
#    $ dnskeygen -H 128 -h -n host.example.org.
#    $ cat Khost.example.org.*.key
#    host.example.org. IN KEY 513 3 157 E91sjfI8pPzhJcaafDDB6g==
#
# Here's a corresponding configuration for ISC BIND 8:
#
#   key host.example.org {
#       algorithm HMAC-MD5.SIG-ALG.REG.INT;
#       secret E91sjfI8pPzhJcaafDDB6g==;
#   };
#
#   zone "example.org" {
#       ...
#       allow-update { key host.example.org; };
#   };
#
# Some information is in the bind-doc.tar.gz shipped with BIND 8 and
# available from http://www.isc.org/sw/bind/

################################
##   End User Configuration   ##
################################

## Our "die" function (think perl)
function die () { echo "$@" 1>&2 ; exit 1 ; }

## Test for needed binaries in the PATH
export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
hash ping cat host ifconfig nsupdate tail perl test || die $0: required binaries not present

## Make sure we can reach the nameserver
ping -c 1 $dnsserver >/dev/null 2>&1 || exit

## Get the old and new IP addresses
old=$(host $hostname $dnsserver | tail -1 | perl -ane'print $F[-1]')
new=$(ifconfig $internet 2>&1 | perl -ne'/inet addr:(\S+)/ and print $1')

## Simple check that we have a new address
test -n "$new" || die $0: could not find IP address

## Ensure there is a change to publish
test "${new}" != "${old}" || exit

## Invoke the correct nsupdate(8), using process substitution to avoid a temporary file
if test "${version}" = "nine" ; then

## Bind 9
nsupdate <( cat <<-BIND9
key ${keyname} ${key}
server ${dnsserver}
update delete ${hostname} A
update add ${hostname} ${ttl} IN A ${new}
send
BIND9
) || die $0: nsupdate failed.

else 

## Bind 8
nsupdate -k ${keydir}:${hostname}. <( cat <<-BIND8
update delete ${hostname}. A
update add ${hostname}. ${ttl} IN A ${new}

BIND8
) || die $0: nsupdate failed.

fi