What is the mac-address of multicast (ipv6)

In IPv4, ff-ff-ff-ff-ff-ff is broadcast address so that this frame can pass layer 2 of all machines.

In IPv6, ARP is not used but ICMPv6 is used to know mac-address by multicasting. In this case, what is mac-address of multicasting??

If mac-address is not matched, this frame cannot pass layer 2 of destination machine. So, I really wonder how multicast packet is passed layer 2 by not using ff-ff-ff-ff-ff-ff.

2 Answers

Ethernet has "multicast" MAC addresses as well – any MAC address with the "group" bit set is technically a multicast address; IPv6 uses the prefix 33:33:*, while IPv4 uses 01:00:5e:*. There are other widely-used prefixes, see this Wikipedia table for details.

For IPv6 multicast addresses, the last 32 bits of the IPv6 address are OR'd with 33:33:00:00:00:00. For example:

• The "all nodes" address ff02::1 is converted to 33:33:00:00:00:01.

• Neighbour solicitations for an example address fe80::4a5d:60ff:fee8:658f are sent to the corresponding Solicited-Node multicast address ff02::1:ffe8:658f, which is converted to Ethernet address 33:33:ff:e8:65:8f.

This is described in RFC 2624 section 7.

1

The function of arp is replace by Neighbour Solicitation in IPv6.

This article explains it best if you understand address allocation.

Ipv6 Neighbour Solicitation

Updated Link because of Blog Refactor:

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