How do you automatically detect a new network card in CentOS 6 / RedHat?

With CentOS 6 everthing is handled by udev now. Go into /etc/udev/rules.d and delete the 70-persistent-net.rules file and reboot. If you open it berfore hand you will most likey see the original NIC MAC listed as eth0 and the new one as eth1.

Now you need to edit /etc/sysconfig/network-scripts/ifcfg-eth0 and manually update to the MAC of your new NIC card.

Deleting the file forces the detection process to run again at boot with no baggage left over from the cloning process, namely the old NIC MAC address(es).

I have to do it with my CentOS 6 clones on VMware ESXi 4.1 all the time. It's a pain kudzu would just handle it in the past with previous versions.

You can use this tool also (This is not a GUI tool, its TUI tool, Text-based User Interface)

[root@localhost ~]# system-config-network-tui

Type above command and press Enter

Then this screen will appear

Select Device configuration and press Enter

Then this screen will appear

Here eth0 refers /etc/sysconfig/network-scripts/ifcfg-eth0

Whatever the edit made in eth0 that will affect to ifcfg-eth0 file

Delete the persistent rules file:

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

Edit ifcfg-eth0:

nano /etc/sysconfig/network-scripts/ifcfg-eth0

REMOVE the HWADDR line altogether (or change it to match your new NIC's MAC address).

Reboot your system:

reboot

If you change the NIC again, just repeat step #1 and # 3.