[CentOS] setup iptables to allow forwarding through eth1

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

http://www.centos.org/docs/5/html/5.2/Deployment_Guide/s1-firewall-ipt-fwd.h...

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?

Regards, Peter