[CentOS] setup iptables to allow forwarding through eth1

Peter Peltonen peter.peltonen at gmail.com
Sun Aug 30 18:47:52 UTC 2009

I have a fresh installed CentOS 5.3 server which should route traffic
between two networks like this:

network A (Internet) -- eth0 (default gw) : server : eth1 -- network B (LAN)

I have set in sysctl.conf

net.ipv4.ip_forward = 1

and routing works fine like this. But when I switch on the iptables
service (with default setup, configured when installing the server),
routing stops working (or at least I cannot ping a server in network A
from network B).  I guess the firewall is stopping it, so I read


and issued the commands

# iptables -A FORWARD -i eth1 -j ACCEPT
# iptables -A FORWARD -o eth1 -j ACCEPT

but that did not help.

So I am asking: what is the correct iptables command to make forwarding work?


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