#319 Associate aliased IP address with server in DMZ (SNAT)

It could be very useful if certain servers in the DMZ
could have different IP addresses associated with them.
Many mail servers do a reverse DNS lookup when
contacted by another mail server and if the IP address
does not match the looked up address the mails are
marked as spam or just dropped.

Our firewall has IP address XXX.YYY.ZZZ.200 and all
servers in the DMZ seem (to the outside) to origin from
that address.

I manually added this:
iptables -t nat -A CUSTOMPOSTROUTING -o eth2 -s
10.0.1.251 -j SNAT --to-source XXX.YYY.ZZZ.251

..so that our mail server (10.0.1.251) externally seem
to have the XXX.YYY.ZZZ.251 address.

[Markus Hoffmann]

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Maybe this is what you're looking for ?

http://mh-lantech.css-hamburg.de/ipcop/download.php?view.154