This reports which interface this multicast group's join request and traffic actually originated from -- Ethernet or satellite -- distinguishing a group requested by a local LAN device from one arriving via the satellite side. This distinction matters a lot on this platform because forwarding a satellite-sourced multicast group back out to Ethernet, or the reverse, has very different bandwidth implications given how constrained the satellite link typically is. For example, a group showing source satellite(2) confirms that stream is consuming scarce inbound satellite bandwidth, unlike one sourced locally from ethernet(1) that never touched the satellite link at all.