Why are some protocol packets fail to be transparently transmitted after the multicast drop-unknown command is configured on an S series switch

After the multicast drop-unknown command is configured on a switch, the switch forwards packets with destination MAC and IP addresses as multicast addresses according to the multicast forwarding table. If a packet matches no multicast forwarding entry, the switch considers it as an unknown multicast packet and drops it.
Some protocol packets, such as OSPF packets, VRRP packets, and IPv6 RA messages, use reserved group addresses as destination MAC and IP addresses and match no multicast forwarding entry. If the switch is configured to drop unknown multicast packets using the multicast drop-known command, the switch drops these protocol packets.
Therefore, do not use the multicast drop-unknown command in a VLAN if the switch needs to transparently transmit protocol packets with reserved group addresses.

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