1. All public NICs must have the same name on all nodes in the cluster
2. Similarly, all private NICs must also have the same names on all nodes
Use component verifications commands like 'nodereach' or 'nodecon' for this purpose. Type cluvfy comp -help on the command prompt. If the 'cluvfy comp nodecon' command is invoked without -i, cluvfy will attempt to discover all the available interfaces and the corresponding IP address & subnet. Then cluvfy will try to verify the node connectivity per subnet.
You can run this command in verbose mode to find out the mappings between the interfaces, IP addresses and subnets. You can check the connectivity among the nodes by specifying the interface name(s) through -i argument
Note : If you metalink support, there is a step by step document *RAC and Oracle Clusterware Best Practices and Starter Kit (Linux) [ID 811306.1]*