iptables and snatting to different networks

Posted by codingfreak on Server Fault See other posts from Server Fault or by codingfreak
Published on 2009-12-23T04:09:40Z Indexed on 2010/04/29 20:07 UTC
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Filed under:

iptables

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nat

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linux

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firewall

                linuxbox (p.q.r.t)
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                    |
 INTERNAL  ------ ABCD ----- INTERNET
(p.q.r.s)                  (m.n.o.k)

ABCD has 3 interfaces connected to linuxbox, INTERNAL N/W, INTERNET.

Linuxbox has a private address (p.q.r.t). At present I am snatting the packets from linuxbox to INTERNET at ABCD.

I have a small doubt regarding the FTP from linuxbox since I have to support ftp from linuxbox to both INTERNAL N/W as well as in INTERNET.

How can I right a rule in iptables present in ABCD where it can decide if the destination ip-address of ftp server is within INTERNAL N/W or in INTERNET and do natting accordingly.

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