Both IPv4 and IPv6 multicast addresses are similar in function. A multicast address is used to send a single packet to one or more destinations. Prefix FF00::/8 is reserved for multicast IPv6 addresses. Multicast addresses can only be destination addresses. There are two types of IPv6 multicast addresses:
- Assigned multicast
- Solicited-node multicast
Assigned multicast addresses are reserved for predefined groups of devices. An assigned multicast address is a single address used to reach a group of devices running a common protocol or service. Assigned multicast addresses are used in context with specific protocols such as DHCPv6.Two common IPv6 assigned multicast groups are following:
- All-nodes multicast group
- All-routers multicast group
All-nodes multicast group This is a multicast group that all IPv6-enabled devices join. IPv6 address ff002::1 is reserved for this group. A packet sent to this group is received and processed by all IPv6 interfaces in the group. Example of this process is RA message to
This is a multicast group that all IPv6-enabled devices join. IPv6 address ff002::1 is reserved for this group. A packet sent to this group is received and processed by all IPv6 interfaces in the group. Example of this process is RA message to the all-node multicast group. When an IPv6 router sends Internet Control Message Protocol version 6 (ICMPv6) RA messages to the all-node multicast group. The RA message informs all IPv6-enabled devices on the network about addressing information, such as the prefix, prefix length, and default gateway.
All-routers multicast group –This is a multicast group that all All routers on the local network segment join. FF02::2 IPv6 address is reserved for this group. A local router becomes a member of this group when it is enabled as an IPv6 router with the ipv6 unicast-routing global configuration command. A packet sent to this group is received and processed by all IPv6 routers on the link or network. IPv6-enabled devices send ICMPv6 Router Solicitation (RS) messages to the all-routers multicast address. The RS message requests an RA message from the IPv6 router to assist the device in its address configuration.
Solicited-Node IPv6 Multicast Addresses
A solicited-node multicast address is like to the all-nodes multicast address. The solicited-node multicast address can be mapped to a special Ethernet multicast address. This allows the Ethernet NIC to filter the frame by examining the destination MAC address without sending it to the IPv6 process to see if the device is the deliberate target of the IPv6 packet.
The Solicited-node multicast is a flooding optimization. If sufficient information was already known to support unicast operation then there would be no point.
The solicited-node multicast is used when there is no information to support unicast operation. The solicited-node allows for the flooded traffic to reach all nodes like broadcast.