Avaya ERS 8600 series, Configuration Manual

Page: 18 / 420

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
Figure 1: IPv6 header on page 18 illustrates the IPv6 header.
Figure 1: IPv6 header
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 2: 128-bit IPv6 address format on
page 19 shows the IPv6 address format.
IPv6 routing fundamentals
18 Configuration — IPv6 Routing November 2010