3Com Switch 8800 Advanced Software V5 Configuration Guide

214 CHAPTER 23: IPV6 BASICS CONFIGURATION
■ Multicast address: An identifier for a set of interfaces (typically belonging to
different nodes), similar to an IPv4 multicast address. A packet sent to a
multicast address is delivered to all interfaces identified by that address.
■ Anycast address: An identifier for a set of interfaces (typically belonging to
different nodes). A packet sent to an anycast address is delivered to one of the
interfaces identified by that address (the nearest one, according to the routing
protocols’ measure of distance).
n
There are no broadcast addresses in IPv6. Their function is superseded by multicast
addresses.
The type of an IPv6 address is designated by the first several bits called format
prefix.
Table 19 lists the mappings between address types and format prefixes.
Unicast address
There are several forms of unicast address assignment in IPv6, including global
unicast address, link-local address, and site-local address.
■ The global unicast address, equivalent to an IPv4 public address, is provided for
network service providers. The structure of such a type of address allows
efficient route prefix aggregation to restrict the number of global routing
entries.
■ The link-local address is used for communication between link-local nodes in
neighbor discovery and stateless autoconfiguration. Routers must not forward
any packets with link-local source or destination addresses to other links.
■ IPv6 unicast site-local addresses are similar to private IPv4 addresses. Routers
must not forward any packets with site-local source or destination addresses
outside of the site (equivalent to a private network).
■ Loopback address: The unicast address 0:0:0:0:0:0:0:1 (represented in the
shortest format as ::1) is called the loopback address and may never be
assigned to any physical interface. Like the loopback address in IPv4, it may be
used by a node to send an IPv6 packet to itself.
■ Unassigned address: The unicast address "::" is called the unassigned address
and may not be assigned to any node. Before acquiring a valid IPv6 address, a
node may fill this address in the source address field of an IPv6 packet, but may
not use it as a destination IPv6 address.
Tabl e 19 Mapping between address types and format prefixes
Type Format prefix (binary) IPv6 prefix ID
Unicast
address
Unassigned address 00...0 (128 bits) ::/128
Loopback address 00...1 (128 bits) ::1/128
Link-local address 1111111010 FE80::/10
Site-local address 1111111011 FEC0::/10
Global unicast
address
other forms -
Multicast address 11111111 FF00::/8
Anycast address Anycast addresses are taken from unicast address space
and are not syntactically distinguishable from unicast
addresses.