From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Brenton <cbrenton@chrisbrenton.org>
Subject: Re: firewalled dns clients
Date: 07 Nov 2003 05:33:12 -0500
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To: Fritz Mesedilla <fritz.mesedilla@overturemedia.com>
Cc: "Netfilter Mailing List (E-mail)" <netfilter@lists.netfilter.org>

On Thu, 2003-11-06 at 22:49, Fritz Mesedilla wrote:
>
> I tried this and nothing happened.
> $IPTABLES -A INPUT -p tcp --sport 53 -j ACCEPT
> even a
> $IPTABLES -A INPUT -p tcp --dport 53 -j ACCEPT

Try:
iptables -t nat -A POSTROUTING -o eth0 -j SNAT --to-source x.x.x.x
iptables -A FORWARD -p udp -i eth1 -s y.y.y.y -d 0/0 --dport 53 -j
ACCEPT
iptables -A FORWARD -p tcp -i eth1 -s y.y.y.y -d 0/0 --dport 53 -j
ACCEPT

x.x.x.x = Firewall's legal external IP address 
y.y.y.y = internal private subnet 
eth0 = external interface (change to eth1 if needed)
eth1 = internal interface (change to eth0 if needed)

HTH,
C