Network / Infrastructure Related Problems

Network Card replacement

1. Shut the system down. Replace the card physically and start the machine.
2. ifconfig would not show up the new interface. If it shows up that you might be all good and skip next steps.
3. ifconfig -a . Find out the new interface that has been created for the new card. Say this is eth1. 
4. Open up a file /etc/sysconfig/network-scripts/ifcfg-eth1. 
5. The file should be similar to other interface file, if exists, say ifcfg-eth0. It's contents would look like 
   

   DEVICE=eth1
   BOOTPROTO=dhcp
   HWADDR=00:08:74:46:D7:E5
   ONBOOT=yes
   DHCP_HOSTNAME=delllap.jesnet
   TYPE=Ethernet

   You can find details of all possible configurations in the CentOS manual.

6. Then restart the network service. service network restart.

7. ifconfig should now show up the new interface eth1.

If the interface names are not coming up correctly, you might want to update the 

/etc/udev/rules.d/70-persistent-net.rules

Refer to http://www.linuxfromscratch.org/blfs/view/development/chapter07/network.html

Further reading (just in case) : http://jeeva.us/Linux/Network