[CentOS] DNAT PREROUTING issue with iptables

Indunil Jayasooriya indunil75 at gmail.com
Tue Sep 25 05:27:34 UTC 2007


Hi,

I have an DNAT ISSUE with PREROUTING.

This is my setup.

I have 2 firewalls running iptables.

Pls asume 1.2.3.4/29 is the internet interace of FIRST firewall.
2.3.4.5/29 is the internet interface of SECOND firewall. it has DMZ zone. in
that DMZ zone, mail server runnig @ 192.168.100.3

Now I want to DNAT port 25 of FISRT firewall (i.e  -  its ip address -
1.2.3.4/29) to the internet ip address ( 2.3.4.5/29) of SECOND firewall.
That firewal DNATs port 25 to mail server @ 192.168.100.3 in DMZ zone.

These are rules I have added.

FIRST firewall (its internet ip address - 1.2.3.4/29) I have addes below
rule.

iptables -t nat -A PREROUTING -p tcp -i eth0 -d 1.2.3.4 --dport 25 -j DNAT
--to-destination 2.3.4.5:25

That should forward port 25 to SECOND firewall. in SECOND firewall, I have
added 2 below rules.

iptables -t nat -A PREROUTING -p tcp -i eth0 -d 2.3.4.5 --dport 25 -j DNAT
--to-destination 192.168.100.3:25

iptables -A FORWARD -p tcp -d 192.168.100.3 --dport 25 -m state --state NEW
-j ACCEPT

Now, it should forward port 25  to  mail server  @  DMZ Zone.

I think I have added these rules properly. But, It does not work.

I checked from outside world . I telneted to port 25 of first firewaal.
Then, It should forward to mail server @ DMZ zone.
But, no responce.

WHY is that?

YOUR IDEAS?






-- 
Thank you
Indunil Jayasooriya
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