network card stop working

[nikgau]

[nikgau]

Sorry guys perhaps I missed the content. I am posting the problem once again.
I have a rhel 4.5 server with two NIC cards one of which is connected to internet (eth0) and other one is connected to intranet(eth1). I have installed the squid proxy server on this and providing the internet connection to some of members of intranet.
Now, whenever I start the server eth0 does not connect to the internet directly I have to execute

ifdown eth0
ifup eth0

then only internet connections works. Sometime the internet connection stops working and again I have to execute the above 2 commands to make it work. What could be the possible reason ? Please provide the solution.