Re: DNAT PREROUTING issue with IPTABLES
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Indunil Jayasooriya wrote:
> SECOND Firewall's default route (gateway) is NOT the FIRST firewall.
> BOTH firewall's default route (gateway) is the router given by our ISP.
Ok, so you understand your problem now?
Assuming the packet arrives at 126.96.36.199 from random external ip (eg.
188.8.131.52), is successfully dnat+rerouted to 184.108.40.206, there again
dnat+reroute to 192.168.x.x. Arrives at smtp server and smtp server
sends a reply to the original sender 220.127.116.11. It does that via it's
default gateway which I assume is 18.104.22.168. 22.214.171.124 sends it via your
ISP's gateway with it's own address of 126.96.36.199 to 188.8.131.52.
But 184.108.40.206 sent the packet 220.127.116.11, not 18.104.22.168, so it discards it.
And that's exactly what Riccardo said when I read his mail now.
The first problem though is that I'm not sure the dnat form 22.214.171.124 to
126.96.36.199 works, the packet would have to leave via the same interface it
came. Maybe this works, I've never tried that. Make sure packets arrive
on the smtp box with tcpdump.
As for the solution, one way would be to SNAT the connection at FW1, but
this wwould cause the smtp box to see as if all the incoming connections
are from 188.8.131.52 and not their real IP's (184.108.40.206).
Actually you should set up custom routing at 220.127.116.11 and not DNAT. You'd
have to mark the packets and then send them to the 18.104.22.168 fw via a
custom route. I'm not sure I could help you with that, never done any
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