forcing outbound address/interface?

i have a linux nat firewall that does SNAT with iptables for an
internal smtp server (only sends outgoing mail). the nat fw has
multiple public ip's, how can i set all outgoing smtp traffic to use a
specific address? all the public ip's use the same gateway. im afraid
mangling the source address will mess up the SNATing.

thanks.

(E-Mail Removed) <(E-Mail Removed)> wrote:

> i have a linux nat firewall that does SNAT with iptables for an
> internal smtp server (only sends outgoing mail). the nat fw has
> multiple public ip's, how can i set all outgoing smtp traffic to use a
> specific address? all the public ip's use the same gateway. im afraid
> mangling the source address will mess up the SNATing.

Hm, I don't understand. If you do SNAT, then you are
already mangling the source address. So if you do

iptables -t nat -A POSTROUTING -p tcp --dport smtp \
-j SNAT --to-source <public smtp ip>

you change the source IP of the outgoing smptp traffic to
<public smtp ip>.


Ciao, Horst
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»When pings go wrong (It hurts me too)« E.Clapton/E.James/P.Tscharn