I have a SQL Server 2008 R2 Standard instance in a "DMZ", so that it can be client-facing. I am trying to have it write its backups to a central location that is within the network. The engineers suggest that they can open a port for me. Hence the question: What port is used by SQL Server to write backups to a remote server?
If you use SMB over TCP directly (ie. disable NetBIOS) then the port used is 445, both UDP and TCP. If you use NetBIOS then it requires 137 both UDP and TCP, 138 UDP and 139 TCP. See Directly Hosting SMB over TCP/IP:
I am doing remote backup by backing-up locally and then copying the bak files to remote storage file share.
I do not think it is much different if to backup directly. Anyway I've checked it with WireShark:
having shown that TCP port 445 was used. Though, depending on Windows version (it was not even clear if your backup will be stored on a device under Windows), TCP port 139 could have been used or whatever the backup application/device/OS is configured to use.
Another question is that a port as such is not sufficient for giving access since it is being "opened" in context of ports, protocols, applications/programs, accounts.