Use the bptestbpcd from your master server and provide an output:
How to test client connections using the bptestbpcd command with Veritas NetBackup
http://seer.entsupport.symantec.com/docs/277901.htm
If your BPCD has already binded to the external interface, you should be able to connect. (if you aren't blocking it by firewall, of course)
One more good reference http://seer.entsupport.symantec.com/docs/321172.htm
If your bpcd isn't running you can force it
by this command: bpcd -standalone