Aggregatable global unicast addresses can be routed globally on the

IPv6 portion of the Internet known as the 6bone (IPv6 backbone).

These types of addresses are equivalent to public IPv4 addresses. As the

name implies, aggregatable global unicast addresses are designed to be

aggregated or summarized to produce an efficient routing infrastruc 

ture. 

Anycast Addressing

An IPv6 anycast address is assigned to more than one interface, typi 

cally belonging to different nodes, with the property that a packet sent

to an anycast address is routed to the  nearest  interface having that

address, according to the routing protocol's measure of distance. 

Anycast addresses, when used as part of a route sequence, permits a

node to select which of several Internet service providers it wants to

carry its traffic. This capability is sometimes called  source selected

policies.  Anycast addressing is implemented by configuring anycast

addresses to identify the set of routers belonging to internet service

providers (for example, one anycast address per Internet service

provider). The anycast addresses can be used as intermediate addresses

in an IPv6 routing header to cause a packet to be delivered by means of

a particular provider or sequence of providers. Other possible uses of

anycast addresses are to identify the set of routers attached to a particu 

lar subnet, or the set of routers providing entry into a particular rout 

ing domain. 

Multicast Addressing

A multicast address is an identifier for a set of interfaces that typically

belong to different nodes. Each multicast group identifies two or more

packet recipients. A particular multicast address can be confined to a

single system, restricted within a specific site, associated with a partic 

ular network link, or distributed worldwide. When a packet is sent to a

multicast address, the protocol delivers the packet to all interfaces iden 

tified by that address.

IPv6 Efficient Hierarchy Addressing and Routing

IPv6 routing is almost exactly like IPv4 routing except for the length of

the address and the subnet mask. Although IPv4 uses a dotted decimal

representation of the network prefix known as the subnet mask, a sub 

net mask is not used for IPv6. Only the prefix length notation is sup 

ported. 

As in the CIDR notation, the prefix length consists of the bits that have

the fixed values or are the bits of the network identifier. For example,

FE80::2AA:FF:FE9A:4CA2/64 indicates that the first 64 bits of the

address are the network prefix. Prefix notation is also used to express

network or subnet identifiers. For example, 21DA:D3::/48 is a subnet. 

The routing in IPv6 mirrors the classless concept, but IPv6 has a well 

defined set of boundaries from which to define sets of address space to

delegate downstream to other people who get Internet connectivity. 

At the level of the Internet backbone where major enterprises and ISP

networks come together, it is necessary to maintain a hierarchical

addressing system similar to the national and internal telephone sys 

4 5