[CentOS] UUID for network cards

Hello,

with CentOS 6, my new server created an UUID entry in ifcfg-eth0 - 
additional to HWADDR entry.

Up to CentOS 5 the connection to the netwark card was defind only by HWADDR.

Now I have a new network card. How can I get the correct UUID?

The server connects correct the network with the updated HWADDR without 
any UUID. Why do I need an UUID?

Thank you for help in advance.

Best Regards
Helmut Drodofsky