If you do not have the UUID (Universal Unique Identifier) identifiers in your ifcfg-xxx files, you can generate these IDs from the command line. Bear in mind each time you run this command for an interface, a new UUID is generated, and presumably the old one becomes invalid.
To generate a UUID:
uuidgen <interface> uuidgen eth0
This will return a value that looks similar to the one below:
You can now add this line to your interface config file (/etc/sysconfig/network-scripts/ifcfg-eth0 in this example)