Hey @MySql Backup & Restore , welcome and thanks for the post!
On a side note, it looks like your user display name is MySQL Backup & Restore, so send me a private message if you e=want it changed (and what I should change it to)!
For your error, it definitely looks like a communication issue. fsIndexedRestore.log and CVD.log should give us a good place to start.
Can you confirm what is opened in your firewall exclusions and how? Is there any filtering done on the executables itself?
I’m thinking it is most likely a port issue, however.
What's interesting on restore for (in most cases, not all) is that the Media Agent initiates the restore on the client. On a backup, the CommServe initiates the backup and communicates with the client-server, which then connects to the media agent. But on restore, the Media Agent typically reaches out to the client in the networking flow. So my bet is that if you try telnet or cvping from the MA to the client, there is a connection failure there or some sort of firewall blocking a connection between those two. It could also be DNS, where the Media Agent cannot resolve the client but the CommServe can..
That might give you some info to start exploring further.