RFC 4605: Forward packets from one downstream interface to the others

4.2.  Forwarding Packets
A proxy device forwards packets received on any downstream interface to to each
downstream interface other than the incoming interface based upon the
downstream interfaces' subscriptions and whether or not this proxy
device is the IGMP/MLD Querier on each interface.
RFC 4605: Forward packets from downstream interface to upstream interface

4.2.  Forwarding Packets
A proxy device forwards packets received on any downstream interface to the upstream interface

If you want to enable this feature:Forward packets from downstream interface to upstream interface
Please add "down_to_up enable" into its config file, default value is disable.
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