Hello Nik14,

Can you review the documentation @ https://documentation.commvault.com/commvault/v11_sp20/article?p=7102_1.htm and tell me if this answers your question?

In short - 8403 can be used as a tunnel port for everything (data + control traffic) but it really depends on your port / network restrictions to be able to give a definitive answer as you may require one/two way network route if direction of traffic is restricted.

Regards
Edd

Hello Nik14, 

It depends on the agent you are using to perform the backup and the network configuration of your environment. The most usual ports are 8400 and 8403 for communication services between client-CommServe. 

Also, you can use the Network Test Tool and check your environment:

https://documentation.commvault.com/commvault/v11_sp20/article?p=7570.htm

Regards