Introduction To Ipv6 Address - 3Com MSR 50 Series Configuration Manual

Introduction to IPv6
Address
c
QoS support
The Flow Label field in the IPv6 header allows the device to label packets in a flow
and provide special handling for these packets.
Enhanced neighbor discovery mechanism
The IPv6 neighbor discovery protocol is implemented through a group of Internet
Control Message Protocol Version 6 (ICMPv6) messages that manages the
information exchange between neighbor nodes on the same link. The group of
ICMPv6 messages takes the place of Address Resolution Protocol (ARP) messages,
Internet Control Message Protocol version 4 (ICMPv4) router discovery messages,
and ICMPv4 redirection messages and provides a series of other functions.
Flexible extension headers
IPv6 cancels the Options field in IPv4 packets but introduces multiple extension
headers. In this way, IPv6 enhances the flexibility greatly to provide scalability for IP
while improving the handling efficiency. The Options field in IPv4 packets contains
40 bytes at most, while the size of IPv6 extension headers is restricted by that of
IPv6 packets.
IPv6 address format
An IPv6 address is represented as a series of 16-bit hexadecimals, separated by
colons. An IPv6 address is divided into eight groups, and the 16 bits of each group
are represented by four hexadecimal numbers which are separated by colons, for
example, 2001:0000:130F:0000:0000:09C0:876A:130B.
To simplify the representation of IPv6 addresses, zeros in IPv6 addresses can be
handled as follows:
Leading zeros in each group can be removed. For example, the
■
above-mentioned address can be represented in shorter format as
2001:0:130F:0:0:9C0:876A:130B.
If an IPv6 address contains two or more consecutive groups of zeros, they can
■
be replaced by the double-colon :: option. For example, the above-mentioned
address can be represented in the shortest format as
2001:0:130F::9C0:876A:130B.
CAUTION: The double-colon :: option can be used only once in an IPv6 address.
Otherwise, the device is unable to determine how many zeros that double-colons
represent when converting them to zeros to restore a 128-bit IPv6 address.
An IPv6 address consists of two parts: address prefix and interface ID. The address
prefix and the interface ID are respectively equivalent to the network ID and the
host ID in an IPv4 address.
An IPv6 address prefix is written in IPv6-address/prefix-length notation, where
IPv6-address is an IPv6 address in any of the notations, and prefix-length is a
decimal number indicating how many bits from the utmost left of an IPv6 address
are the address prefix.
IPv6 address classification
IPv6 addresses fall into three types: unicast address, multicast address, and anycast
address.
IPv6 Overview 657