I have got stuck in this configuration for a while and I really dont know how to make it work. Please help me to solve out this problem.

I have the following system:
eth0 eth1 eth0 eth1 eth0 eth0
x.240.5 x.240.1 x.240.2 x.240.3 x.242.3 x.242.1

I could not ping from PC1 and PC2 to PC3 and PC4. So, at the beginning, I tried to run this
eth1 eth1 eth0 eth0
x.240.2 x.240.3 x.242.3 x.242.1
Using the configuration given on http://www.iwpcs.co.uk/simple_net_setup.html for PC2 and http://www.iwpcs.co.uk/ics.html for PC3, I made it worked. Then I added the PC1, from PC1 I can not ping PC2, PC3 and PC4.

From PC1, I ping 240.1 on eth1 of PC2 and then watch the tcpdump on that same eth1. I got a "arp who-has tel".

Could you help me out please? I wonder if this is the problem of iptables but I am really not sure.
Thanks a lot and have a nice day,
Best regards,

Dinh Tran