IPv6 header

The IPv6 header basic length is fixed at 40 octets (bytes) and it contains the following fields:
Table 1. Fields in the IPv6 header

Field

Size in bits

Ver—Internet Protocol version number, with a value of 6

4

DS byte—Traffic class field, similar to Type of Service in IPv4

8

Flow label—identifies traffic flow for additional Quality of Service (QoS)

20

Payload Length—Unsigned integer, the length of the IPv6 payload

16

Next header selector—identifies the next header

8

Hop limit unsigned integer—decrements by 1 each time a node forwards the packet (nodes discard packets with hop limit values of 0)

8

Source address

128

Destination address

128

The following figure illustrates the basic IPv6 header, without extension headers.

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IPv6 header
IPv6 header