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Old 02-17-2010, 08:37 AM   #1
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iptables routing packets on the same sub-network


I am running into trouble while trying to set-up a iptables routing policy. I have two machines on the same sub-network ( One of the machines is used as a default gw for the other ( is a gateway for and is a gw for There is no explanation for why the is in the middle -- can go straight to, but is is like that for now.

I am trying to find an iptable rule to be executed on the machine to route the packets. I was trying something like:

iptables -A FORWARD -i eth0 -s -o eth0 -j ACCEPT
but it doesn't seem enough. I am running openwrt on

Any ideas? Thanks
Old 02-17-2010, 11:27 AM   #2
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I think you need to explicitly tell 254 that gw to 142 is 250. Also, check if forwarding is on in /proc/sys/net/ipv4/ip_forward
Old 02-17-2010, 12:21 PM   #3
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In fact this is the other way around -- 254 is the default gw of .250 (and 250 is the one of 142 even if it should be 254 in 'normal conditions').

The forwarding flag is set to 1. If I put a 'normal' router on the place of the OpenWRT it works straightforward. That's why I think it is a iptables related problem.


Last edited by Evstrati; 02-17-2010 at 12:22 PM. Reason: typo
Old 02-17-2010, 01:50 PM   #4
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So my guess was correct. It works with

iptables -A forwarding_wan -s -o eth0.1 -j ACCEPT
I was not putting the correct forward chain (FORWARD instead of forwarding_wan). It is a bit weird, but it works...

Thanks anyway


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