You can define the source port range that Branch Gateway uses when registering with Communication Manager using the following CLI commands:
set registration source-port-range
show registration source-port-range
set registration default source-port-range
If you do not specify the source port range, Branch Gateway selects a port within the default range of 1024 through 65535.
For more information about these commands, see Avaya Branch Gateway G450 CLI Reference.