IPv6 Multicast Address Format
IPv6 Multicast Address Format

Address Type

The first 8 bits of any IPv6 multicast address are always all turned on:

When we translate the binary into hexadecimal we get:

Pro Tip: When we see the first two nibbles of an address are ff, we immediately know it must be a multicast address.

Flags Field

The bits in the Flags field are used for the following:

0 = Reserved for future use and must be set to 0.

R = 0 Rendezvous Point not embedded
R = 1 Rendezvous Point is embedded

P = 0 Prefix not embedded
P = 1 Prefix is embedded

T = 0 Well Known Address
T = 1 Temporary Address

     Rendezvous Point – A router that is configured to organize a multicast group’s traffic flow. RPs will be discussed in more detail in a future lesson.
     Well-Known Address – These addresses are registered with IANA for specific uses. For example, ff02::1 is always the multicast for all nodes on the local link. Well-Known Addresses are discussed in a future lesson.
     Temporary Address – Not registered with IANA and is assigned by an administrator.

Scope Field

The Scope field denotes where the multicast packets can travel to. Scope values include:
1 – Node
2 – Link
3 – Realm
4 – Administration
5 – Site
8 – Organization
e – Global

Group ID

The last 112 bits of the multicast address identifies a specific multicast group. This field can contain a Well-Known Address or a Temporary address.

RFC 7371: Updates to the IPv6 Multicast Addressing Architecture
RFC 7346: IPv6 Multicast Address Scopes

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