H3C Technologies H3C S3600 Series Switches - Manual (Page 1093)

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Enhanced neighbor discovery mechanism
The IPv6 neighbor discovery protocol is implemented by a group of Internet Control Message Protocol
Version 6 (ICMPv6) messages. The IPv6 neighbor discovery protocol manages message exchange
between neighbor nodes (nodes on the same link). The group of ICMPv6 messages takes the place of
Address Resolution Protocol (ARP), Internet Control Message Protocol Version 4 (ICMPv4), and
ICMPv4 redirect messages to provide 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 processing efficiency.
The Options field in IPv4 packets contains only 40 bytes, while the size of IPv6 extension headers is
restricted by that of IPv6 packets.
Introduction to IPv6 Address
IPv6 addresses
An IPv6 address is represented as a series of 16-bit hexadecimals, separated by colons. An IPv6
address is divided into eight groups, 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:
z 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.
z 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.
The double-colon :: can be used only once in an IPv6 address. Otherwise, the device is unable to
determine how many zeros the double-colon represents when converting it to zeros to restore the IPv6
address to a 128-bit 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
left of an IPv6 address are the address prefix.
IPv6 address classification
IPv6 addresses mainly fall into three types: unicast address, multicast address and anycast address.
z Unicast address: An identifier for a single interface, similar to an IPv4 unicast address .A packet
sent to a unicast address is delivered to the interface identified by that address.