On IPv6 networks, a packet can be directed to an individual machine or multicasted to a set of hosts. When a packet is sent to an IPv6 multicast address from a machine on the local network, that packet is delivered to a subset or all machines on that network.
If the packet that is sent to the multicast address is an ICMP Echo Request packet, the machines on the network will receive this ICMPv6 echo request packet and send an ICMP echo reply packet back. When all the machines on a network respond to this ICMPv6 echo request, the result can be severe network congestion or outages.
Network devices always respond to the IPv6 ICMP packets sent to a multicast address. However, you can disable the processing of IPv6 ICMP packets sent to a multicast address on the device. On disabling the ICMP multicast processing, all the packets containing ICMP sent to multicast addresses are dropped when the packets reach the control plane.