When a backup is performed, Amanda will use a source port on the Amanda server to make a connection with the client on the client’s port 10080. Each different client that Amanda connects with is performed through the same source port on the Amanda server. Additional source ports are opened on the Amanda server when Amanda requires additional connections to the same client as would occur if more than one Backup Set is run at the same time and contains the same client(s) or if Parallel Backups (Client) on Backup|how is set to a number greater than 1 for any Backup Set.
The source port range that Amanda Enterprise uses by default is from port 700 to 710 up to version 3.5 and 800 to 840 for the version 3.6 and later. Amanda will not use a port number that is already assigned by the IANA. If this does not allow enough available source ports for the Amanda server given the backups being performed, the source port range can be increased.
The Amanda Server source port range can be configured by the Ports for Parallel Backups field from the Backup|how page as in earlier versions, but the range is enforced by amanda-security.conf. The file at /etc/amanda-security.conf must be modified so that its tcp_port_range matches the configuration that is set on the Backup|how page.