I have this rules set in my firewall, it is working for me.

$IPT -A OUTPUT -o $EXT -p tcp --sport $UNPRI --dport 53 -j ACCEPT

$IPT -t nat -A PREROUTING -i $EXT -d $EXT_IP1 -p tcp --dport 25 -j DNAT --to $INT_IP1
$IPT -A FORWARD -p tcp --dport 25 -d $INT_IP1 -j ACCEPT

I am also using REdhat 7.3 Kernel 2.4.18-3 and iptables 1.2.7

----- Original Message -----

From: David F. Strauch

To: netfilter@lists.netfilter.org

Sent: Wednesday, October 09, 2002 10:17 PM

Subject: Bad argument `53'

Hello Everyone

By reading New Riders “Linux Firewalls” by Robert L. Ziegler I’m just starting to study iptables. I have a stand-alone firewall offline and off the local network running RHL 7.3 with Kernel 2.4.18-3 and iptables 1.2.5.

I’ve just started writing the script to allow DNS Loopkups as a client with the following:

if [ "$CONNECTION_TRACKING" = "1" ]; then

    iptables -A OUTPUT -o $INTERNET -p udp \

             -s $IPADDR --sport $UNPRIVPORTS \

             -d $NAMESERVER --dport 53 \

             -m state --state NEW -j ACCEPT

fi

iptables -A OUTPUT -o $INTERNET -p udp \

         -s $IPADDR --sport $UNPRIVPORTS \

         -d $NAMESERVER --dport 53 -j ACCEPT

iptables -A INPUT -i $INTERNET -p udp \

         -s $NAMESERVER --sport 53 \

         -d $IPADDR --dport $UNPRIVPORTS -j ACCEPT

When I execute the script with sh /etc/rc.d/rc.firewalls I receive Bad argument `53' for every instance of either --dport 53 or --sport 53. I’ve also tried --destination-port and --source-port with out any success.

Can anyone shed some light on my problem?

Dave