Header Format

The following figure shows the elements that appear in the IPv6 header and the order in which the elements appear.

Figure 1–1 IPv6 Header Format

The following list describes the function of each header field.

• Version – 4-bit Version number of Internet Protocol = 6.

• Traffic Class – 8-bit traffic class field. See Traffic Class.

• Flow Label – 20-bit field. See IPv6 Quality-of-Service Capabilities.

• Payload Length – 16-bit unsigned integer, which is the rest of the packet that follows the IPv6 header, in octets.

• Next Header – 8-bit selector. Identifies the type of header that immediately follows the IPv6 header. Uses the same values as the IPv4 protocol field. See Extension Headers.

• Hop Limit – 8-bit unsigned integer. Decremented by one by each node that forwards the packet. The packet is discarded if Hop Limit is decremented to zero.

• Source Address – 128 bits. The address of the initial sender of the packet. See IPv6 Addressing.

• Destination Address – 128 bits. The address of the intended recipient of the packet. The intended recipient is not necessarily the recipient if an optional Routing Header is present.