Multicast routing

I have an device running openWRT. It is configured with a number of LAN ports, and one WAN port. A VPN has been configured over the WAN interface, and the WAN interface itself runs over a cellular link.

The LAN contains a multicast video source. To preserve cellular bandwidth, I am looking into whether it is possible to only stream multicast traffic over the cellular WAN link when we have at least one multicast listener on the remote network. I was looking into whether I could do this with IGMP snooping, but suspect PIM might be needed on the openWRT device itself....?

Can anyone shed any light here? I'm finding multicast to be a bit of a black there a solution?

From what I recall of multicast, you need an RP on your remote and local networks so that multicast traffic is only spanned when a remote client tries to join the multicast group. It's definitely a job for PIM, rather than some sort of routing rule.

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