IPv6 Multicast Address

IPv6 Multicast Address
In the IPv6 world, there is no such thing as broadcast traffic because it is all multicast traffic—no
more broadcast storms. IPv6 multicast traffic has a prefix of FF00::/8 and is used as an identifier
for a set of interfaces that want to receive the same packets. This is very similar to the way multicast
works in the IPv4 world, with one exception. IPv6 multicast traffic can be limited to a certain
scope. The octet after the initial 0xFF prefix defines the public/private nature and scope of the
multicast address. The first nibble of the octet determines if this is a transient (0001) or permanent
(0000) multicast address, with the first three bits always set to 0. A permanent multicast address
is a well-known or IANA-assigned address. A transient address is locally assigned. The second
nibble determines the scope of the multicast address and can be one of the following:
 Interface-local, for loopback multicast transmissions only (0001–1)
 Link-local (0010–2)
 Subnet-local (0011–3)
 Admin-local (0100–4)
 Site-local (0101–5)
 Organization-local (1000–8)
 Global (1110–E)
The remaining 112 bits are used for the multicast group ID. This means that you can have
millions of multicast groups. The following are the special reserved multicast addresses used to
identify specific functions:
 FF01::1—All nodes within the interface-local scope (only within this device)
 FF02::1—All nodes on a local link (link-local scope)
 FF01::2—All routers within the interface-local scope
 FF02::2—All routers on a local link
 FF05::2—All routers in the site (site-local scope)
 FF02::1:FFXX:XXXX—Solicited-node multicast address, where XX:XXXX is the lowerorder
24 bits of the IPv6 address of an interface.
The TTL—time to live—value is not used in IPv6 multicast to define scope.
Exam Essentials 73
The solicited-node multicast addresses are used in neighbor solicitation messages to assist
with neighbor discovery. An IPv6 node must join the associated solicited-node multicast group
for every unicast or anycast address assigned. Neighbor solicitation messages are not covered
because they are beyond the scope of this study guide.