The Ipv6 Header; Ipv6 Addresses - Avaya 4524GT Configuration Manual

The IPv6 header

The IPv6 header contains the following fields:
• a 4-bit Internet Protocol version number, with a value of 6
• an 8-bit traffic class field, similar to Type of Service in IPv4
• a 20-bit flow label that identifies traffic flow for additional Quality of Service (QoS)
• a 16-bit unsigned integer, the length of the IPv6 payload
• an 8-bit next header selector that identifies the next header
• an 8-bit hop limit unsigned integer that decrements by 1 each time a node forwards the
packet (nodes discard packets with hop limit values of 0)
• a 128-bit source address
• a 128-bit destination address

IPv6 addresses

IPv6 addresses are 128 bits in length. The address identifies a single interface or multiple
interfaces. IPv4 addresses, in comparison, are 32 bits in length. The increased number of
possible addresses in IPv6 solves the inevitable IP address exhaustion inherent to IPv4.
The IPv6 address contains two parts: an address prefix and an IPv6 interface ID. The first 3
bits indicate the type of address that follows.
Figure 6: IPv6 address format
Figure 6: IPv6 address format
An example of a unicast IPv6 address is 1080:0:0:0:8:8000:200C:417A
Interface ID
The interface ID is a unique number that identifies an IPv6 node (a host or a router). For
stateless autoconfiguration, the ID is 64 bits in length.
In IPv6 stateless autoconfiguration, the interface ID is derived by a formula that uses the link
layer 48-bit MAC address. (In most cases, the interface ID is a 64-bit interface ID that contains
the 48-bit MAC address.) The IPv6 interface ID is as unique as the MAC address.
Configuration — System
on page 31 shows the IPv6 address format.
IPv6 management
April 2011 31