Chapter 1 IPv6 Address Configuration
Hex
Decimal
Value
13
D
Unallocated
14
E
Global range
15
F
Reserved
l
Group ID field
The 112-bit multicast ID field identifies a multicast group within a specified range
permanently or temporarily.
3.
Anycast Address
A multicast address can be shared by many nodes in a sense. All the nodes of the
members of a multicast address expect to receive all the packets sent to this address.
A router connecting to five different local Ethernet networks shall forward a copy of
these multicast packets to each network respectively (supposing at least one node of
each network subscribes to this multicast address).
Anycast addresses are similar to multicast addresses. Although the two are in the
same case that an anycast address can be shared by multiple nodes, only one node
of an anycast address expects to receive the packet sent to the anycast address.
Anycast is helpful in providing services, especially those requiring no relationship
between client and server, such as, a domain name server and a time server.
A domain name server is nothing but a name server, which provides the same
performance whether it is located closely or remotely.
Similarly, a closely located time server is preferable in terms of accuracy. Therefore,
when a host sends a request to an anycast address to obtain information, it is the
nearest server associated to this anycast address that shall respond.
Anycast addresses are allocated outside of the normal IPv6 unicast address space.
Anycast addresses cannot be distinguished from unicast addresses in their forms, and
each member of an anycast address shall be explicitly configured to identify an anycast
address.
Address Expression Way
An IPv4 address is expressed in four parts separated by dots, that is, four numbers
separated by dots. The following are some legal IPv4 addresses expressed by decimal
integer: 0.5.3.1, 127.0.0.1, 201.199.244.101.
An IPv4 address is expressed as a group of four 2-bit hex integers or four 8-bit binary
integers, of which the latter one is seldom used.
The length of an IPv6 address is four times greater than an IPv4 address, and the
complicacy of expression for an IPv6 address is also four times greater than an IPv4
address. An IPv6 address can be basically expressed as X:X:X:X:X:X:X:X, among which
X is 4-bit hex integers (16-bit). Each number contains four bits, each integer contains four
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