Simple DNS check script

check-dns.sh

#! /bin/sh

# Simple DNS check script
#
# Use it to test forward and reverse DNS entries for the given IP address.
# It requires the dnsutils package which contains the dig command.

IP="$1"

if [ -z "$IP" ]; then
	echo "Usage: $0 {ip-address}"
	echo ""
	echo "Example: $0 192.168.1.42"
	exit 1
fi

IP2DOMAIN=$(dig +short -x $IP)
if [ -z "$IP2DOMAIN" ]; then
	echo "Missing reverse zone entry"
	exit 1
fi

DOMAIN2IP=$(dig +short $IP2DOMAIN)
if [ -z "$DOMAIN2IP" ]; then
	echo "Missing forward zone entry ($IP2DOMAIN)"
	exit 1
fi

if [ "$IP" != "$DOMAIN2IP" ]; then
	echo "Mismatching forward zone entries for $IP2DOMAIN: $IP vs $DOMAIN2IP"
	exit 1
fi

echo "OK"