BPCD logs would have the information about the Network interface ( IP's) used for connections, enable them on Media servers and Client both.
Please run the following commands and the results will show which IP NetBackup is using to connect for the backup
On Master or Media => /usr/openv/netbackup/bin/admincmd/bptestbpcd -client client_name -verbose
On Client => C:\Program Files\Veritas\NetBackup\bin\bptestnetconn
You can also check from Windows Client Server - Open Resource Monitor => Network => check for bpbkar process => Address Column should show you the IP/hostname its using to connect media server
I like @Tape_Archived idea. Should be fairly easy to write a small script that loops thru all clients, to prove what network connection they are using
My suggestion is to use netstat.Netstat will provide you with a quick overview from where connected client are connection from. When I say "connected", I mean a client that is active communicating with master/media server.
# sudo netstat -pt
look for the "foregin address".