In Redhat 7.2 you can use NEAT (NEtwork Administration Tool) to configure your NIC and enter all of your IP information; just type neat in a term window. If you have a problem, give us more to work with:
-concise description of the problem
-troubleshooting steps you've taken so far
-make and model of network card
-description of your connection (cable, DSL, direct connection to modem or though a router, etc.