Header Format

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

Figure 14-1 IPv6 Header Format

The following list describes the function of each header field.

• Version - 4-bit Internet protocol version number = 6

• Priority - 4-bit priority value (see "Priority")

• Flow Label - 24-bit field (see "IPv6 Quality-of-Service Capabilities")

• Payload Length - 16-bit unsigned integer, which is the rest of the packet following the IPv6 header, in octets

• Next Header - 8-bit selector. Identifies the type of header immediately following the IPv6 header. Uses the same values as the IPv4 protocol field (see "Extension Headers").

• Hop Limit - 8-bit unsigned integer. Decremented by 1 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 (not necessarily the recipient if an optional Routing Header is present)