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


Hello,

I am running into trouble while trying to set-up a iptables routing policy. I have two machines on the same sub-network (xxx.xxx.153.0). One of the machines is used as a default gw for the other (xxx.xxx.153.250 is a gateway for xxx.xxx.153.142 and xxx.xxx.153.254 is a gw for xxx.xxx.153.250). There is no explanation for why the xxx.xxx.153.250 is in the middle -- xxx.xxx.153.142 can go straight to xxx.xxx.153.254, but is is like that for now.

I am trying to find an iptable rule to be executed on the xxx.xxx.153.250 machine to route the packets. I was trying something like:

Code:
iptables -A FORWARD -i eth0 -s xxx.xxx.153.142 -o eth0 -j ACCEPT
but it doesn't seem enough. I am running openwrt on xxx.xxx.153.250

Any ideas? Thanks
E
 
Old 02-17-2010, 11:27 AM   #2
sarin
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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
Evstrati
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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.

Thanks

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

Code:
iptables -A forwarding_wan -s xxx.xxx.153.142 -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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