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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  Internet Protocol Version 6 (IPv6) / IP Next Generation (IPng)                      9  IPv6 Addressing

IPv6/IPv4 Address Embedding 1 2 3 4 5 IPv6 Autoconfiguration and Renumbering

Well-Known Multicast Addresses

The Transient flag allows for explicit determination of which multicast addresses are available for normal use compared to which are set aside as “well-known”. Several predefined well-known multicast addresses are defined, by setting aside certain Group IDs that are used for a number of different scope ID values. Table 66 shows these values; the “x” in the multicast address pattern is the hexadecimal digit corresponding to the 4-bit scope ID field.

The “All Nodes” and “All Routers” multicast addresses enable the equivalent function of what broadcast used to perform in IPv4. Again, the concept of scope is important in a multicast of this type because we don't want to try to send a message to “all nodes” on the global Internet, for example. So, when the “all routers” address is used with a scope value of 2, it means “all routers on the local link”. If it is used with a value of 5, it means “all routers in this site”.

Table 66: Important IPv6 “Well-Known” Multicast Addresses

Multicast Address Pattern	Valid Scope Values (decimal)	Designation	Description
FF0x:0:0:0:0:0:0	0 to 15	Reserved	All multicast addresses where the 112-bit Group ID is zero are reserved.
FF0x:0:0:0:0:0:1	1, 2	All Nodes	When the Group ID is equal to exactly 1, this is a multicast to all nodes. Both node-local (FF01:0:0:0:0:0:1) and link-local (FF02:0:0:0:0:0:1) “all nodes” multicast addresses are possible.
FF0x:0:0:0:0:0:2	1, 2, 5	All Routers	When the group ID is equal to exactly 2, this designates all routers within a specific scope as the recipients. Valid scope values are node-local, link-local and site-local.

IPv6/IPv4 Address Embedding 1 2 3 4 5 IPv6 Autoconfiguration and Renumbering

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