NOTE -: It is always recommended to use the dns configuration for the SCAN. This can be used for testing purpose.
If you do not have a proper dns server setup and wish to install RAC without the dns server configuartion , then the following workaround can be tried -:
Rename the file resolv.conf on the all the nodes of the cluster and then execute the runcluvfy.sh
[grid@rac1 grid]$ ./runcluvfy.sh stage -pre crsinst -n rac1,rac2 -verbose
Performing pre-checks for cluster services setup
Checking node reachability...
>>>>>>Here is the output when it checks for the resolv.conf consistency
Checking consistency of file "/etc/resolv.conf" across nodes
File "/etc/resolv.conf" does not exist on any node of the cluster. Skipping further checks
File "/etc/resolv.conf" is consistent across nodes
Check: Time zone consistency
Result: Time zone consistency check passed
Pre-check for cluster services setup was successful.
[grid@rac1 grid]$