Output of the Gaia Clish command "show pim joins" shows that the Security Gateway registers the multicast source even if the Multicast Source does not match the Security Gateway's interfaces subnets.
show pim joins
(<Multicast_Source>, <Multicast_Group>), 00:36:46/13:28:22, RP: <Rendezvous_Point_IP_address>
Register source: <Security_Gateway_IP_address>, Register destination: <Rendezvous_Point_IP_address>
Incoming interface: Eth-<x>, RPF neighbor: <Downstream_Multicast_Neighbor>
Outgoing interface list:
Output of the Expert mode command "ip mroute" shows in the list of outbound interfaces "Oifs" both "pimreg0" and the physical interface facing the Multicast client.
[Expert@HostName:0]# ip mroute
(<Multicast_Source>, <Multicast_Group>) Iif: Eth-<x> Oifs: pimreg0 Eth-<y>
If the Rendezvous Point replies with a "register-stop", then the Security Gateway will continue sending "null-register" messages to the Rendezvous Point every 60 seconds.
The Security Gateway does not check whether the Multicast Source is a local subnet before registering the Multicast Group to the Rendezvous Point.