GRE tunnel and multicast
GRE tunnels support multicast traffic.
GRE tunnels and how they transmit multicast packets
Links:
https://www.cisco.com/c/en/us/support/docs/ip/ip-multicast/43584-mcast-over-gre.html
https://forum.networklessons.com/t/gre-tunnel-key/10667/6?u=lagapides