I have 2 NICs. One is built-in and the other is PCI. I am connected on a network with internet connection. I've configured the PCI(eth1) to connect via internet successfully. But when i configured the built-in (eth0) interface, eth1 can no longer connect via internet but can ping its gateway IP. I found out that when I ping outside connection e.g. yahoo.com, the system uses the eth0 as the external interface connected via internet when in fact, it's the eth1 thats connected via internet.

I prefer to use the eth1 as my interface for my primary internet connection and eth0 for sharing the access to other PCs in the network. Is there a way around with this? Or is it possible to swap the ethx ID?

It sounds like your default gateway is getting screwed up and Linux thinks it's supposed to be routing Internet traffic through eth0 (device names like eth0 and eth1 are just labels -- they're not special in any way). Can you post the output of "netstat -rn" when you have both NICs up. In particular look for where the 0.0.0.0 route is set to go.

Yes, you are right... I got it fix myself... tnx for the tip. What actually happen was, when i added the eth1 there exist 2 gateways because the 2 IPs are of different IP blocks (eth0: 192.168.1.XXX, eth1 192.168.254.XXX). I just removed the gateway IP of eth1 since it's the gateway itself. I also found that out in your suggestion to check using netstat -rn and I saw 2 gateways confusing linux.

I am now on the go to share the internet in my network.... Thanks again... your tip did help a lot... whew!!! God bless!