Chapter 3. IPv6 Addressing
An IPv4 address has 32 bits and is familiar. An IPv6 address has 128 bits and looks wild. Extending the address space was one of the driving reasons to develop IPv6, along with optimization of routing tables, especially on the Internet. This chapter will help you become familiar with the extended address space and will also explain how IPv6 addressing works and why it has been designed the way it is. The IPv6 addressing architecture is defined in RFC 2373, which obsoletes RFC 1884.
Address Types
IPv4 knows unicast, broadcast, and multicast addresses. With IPv6, the broadcast address is not used anymore; multicast addresses are used instead. This is good news because broadcasts are a problem in most networks. The anycast address, a new type of address introduced with RFC 1546, is now used with IPv6.
Unicast, Multicast, and Anycast Addresses
An IPv6 address can be classified into one of three categories:
- Unicast
A unicast address uniquely identifies an interface of an IPv6 node. A packet sent to a unicast address is delivered to the interface identified by that address.
- Multicast
A multicast address identifies a group of IPv6 interfaces. A packet sent to a multicast address is processed by all members of the multicast group.
- Anycast
An anycast address is assigned to multiple interfaces (usually on multiple nodes). A packet sent to an anycast address is delivered to only one of these interfaces, usually the nearest one.
Some General Rules
IPv6 addresses ...
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