Yesterday I was working on an SQL cluster and part of the job was to change the IP address. Doing so caused the application dependent on the cluster to fail. I was required to make a registry changes so the SQL server would listen on the new IP address. What helped me determine the issues and resolve it quickly was running 'netstat -a -n' from the command prompt and looking at what IP address the SQL server was listening on. 'netstat -a -n' is a handy command worth running on secure servers as part of a schedule so you can view what ports/services your server is open to.

Cheers
Ryan Partington