From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chinh Nguyen <cnguyen@certicom.com>
Subject: Re: Dual-home and forward outgoing requests
Date: Thu, 02 Mar 2006 10:24:50 -0500
Message-ID: <44070E42.6000808@certicom.com>
References: <a46d47540603020533v6093ac9et4a1f3677e0f490cc@mail.gmail.com>
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Andy Lego wrote:
> Hello,
> 
> I have a dual-homed network. Is there any way to tell iptables to
> forward all requests for specific service, that come from one
> interface, to go back out on the same interface?
> 
> Right now I have simply:
> 
> -A POSTROUTING -o eth0 -j MASQUERADE
> -A POSTROUTING -o eth1 -j MASQUERADE
> 
> So, what am I missing?
> 
> Thank you.
> 
> --
> http://legoandy.com
> 
Not sure what you mean. Say your device is 10.0.1.5, do you mean that if someone
was to telnet to 10.0.1.5 you would forward it to 10.0.1.10 (10.0.1.0/24 is on
eth0)?

The simplest is to have ip_forwarding on. Then add DNAT and MASQUERADE rules.
Linux routing should take care of the rest.

iptables -A PREROUTING -t nat -p tcp -s 10.0.1.0/24 --dport 23 -j DNAT --to
10.0.1.10
iptables -A POSTROUTING -t nat -j MASQUERADE