Lets say due to N/W or Security issues client is not able to connect to server or vice versa. How do you troubleshoot?

First I will look to ensure that port settings are proper on server and client Network utility for connections. ODBC is properly configured at client end for connection ——Makepipe & readpipe are utilities to check for connection. Makepipe is run on Server and readpipe on client to check for any connection issues.