OpenVPN DNS update (learn-address) for OpenWrt (Can be changed to support others) - Requires knot-nsupdate and knot-dig

openvpn-dnsupdate.sh

#!/usr/bin/env ash

# For use with OpenVPN learn-address (and other things you adapt it to)
# Takes the following as paramters:
# openvpn-dnsupdate.sh operation address hostname
# Example: openvpn-dnsupdate.sh update 10.8.1.50 test.pyronexus.lan
# This creates an A record and a PTR for the IP 10.8.1.50 to test.pyronexus.lan

# This will replace any hostname provided by OpenVPN and will rewrite it to your FWDZONE specified below.
# E.g. test.test.pyronexus.com would be rewritten to test.vpn.pyronexus.lan with the config below.

# original script by http://openvpn.net/archive/openvpn-users/2005-08/msg00146.html
# contribued by Charles Duffy <cduffy@xxxxxxxxxxx> Thu, 11 Aug 2005 19:07:45 -0500
# edited by NotoriousPyro  <PyroNexus.com> 11/05/2017

DNSSERVER="pyronexus.lan"			## your DNS server
FWDZONE="vpn.pyronexus.lan"		## forward resolution zone (ie. vpn.company.com) 
REVZONE="1.8.10.in-addr.arpa"	## reverse resolution zone (ie. "1.0.0.in-addr.arpa") 
NSUOPTS=""						## extra arguments for nsupdate (ie. "-k /path/to/key") 

if [ -n "$DEBUG" ] ; then
	NSUOPTS="$NSUOPTS -d"
	set -x
fi

reverseRecord() {
	echo $1 | sed -re 's/^([0-9]+).([0-9]+).([0-9]+).([0-9]+)$/\4.\3.\2.\1.in-addr.arpa./'
}

addRecord() {
	local ADDRESS="$1"
	local CN="$2"
	local TEMPFILE=$(mktemp /tmp/nsupdate.XXXXXX)
	local REVERSE=$(reverseRecord $ADDRESS)

	cat >$TEMPFILE <<EOF
server $DNSSERVER
zone $FWDZONE
update delete ${CN}. A
update add ${CN}. 3600 A $ADDRESS
send
EOF
	if [ -n "$DEBUG" ] ; then cat $TEMPFILE; fi
	knsupdate $NSUOPTS $TEMPFILE
	cat >$TEMPFILE <<EOF
server $DNSSERVER
zone $REVZONE
update delete $REVERSE PTR
update add $REVERSE 3600 PTR $CN.
send
EOF
	if [ -n "$DEBUG" ] ; then cat $TEMPFILE; fi
	knsupdate $NSUOPTS $TEMPFILE
	rm -f $TEMPFILE
}

removeRecord() {
	local ADDRESS="$1"
	local CN="$2"
	local TEMPFILE=$(mktemp /tmp/nsupdate.XXXXXX)
	local REVERSE=$(reverseRecord $ADDRESS)

	cat >$TEMPFILE <<EOF
server $DNSSERVER
zone $FWDZONE
update delete ${CN}. A
send
EOF
	if [ -n "$DEBUG" ] ; then cat $TEMPFILE; fi
	knsupdate $NSUOPTS $TEMPFILE
	cat >$TEMPFILE <<EOF
server $DNSSERVER
zone $REVZONE
update delete $REVERSE PTR
send
EOF
	if [ -n "$DEBUG" ] ; then cat $TEMPFILE; fi
	knsupdate $NSUOPTS $TEMPFILE
	rm -f $TEMPFILE
}

getCN() {
	local IPADDR=$1
	local FULLNAME=$(kdig +short -x ${IPADDR} )
	if [ -n "$FULLNAME" ] ; then
		echo $FULLNAME | sed -re 's/.$//'
		return 0
	else
		return 1
	fi
}

OPERATION=$1
ADDRESS=$2
CN=$(echo "$3" | cut -d "." -f 1 | sed "s|$|.$FWDZONE|")

REVERSE=$(reverseRecord $ADDRESS)

case "$OPERATION" in
	add|update)
		addRecord "$ADDRESS" "$CN"
	;;
	delete)
		CN=$(getCN "$ADDRESS")
		removeRecord "$ADDRESS" "$CN"
	;;
	*)
		echo "ERROR: don't know operation "$OPERATION"."
		exit 1
esac

return 0