Standard IPv6 Headers

IPv6 packet headers contain many of the fields found in IPv4 packet headers; some of these fields differ from IPv4. (See Figure 13.)

The 40-byte IPv6 header consists of the following eight fields:

Version—Indicates the version of the Internet Protocol.
Traffic class—Previously the type-of-service (ToS) field in IPv4, the traffic class field defines the class-of-service (CoS) priority of the packet. However, the semantics for this field (for example, DiffServ code points) are identical to IPv4.
Flow label—The flow label identifies all packets belonging to a specific flow (that is, packet flows requiring a specific class of service [CoS]); routers can identify these packets and handle them in a similar fashion.
Payload length—Previously the total length field in IPv4, the payload length field specifies the length of the IPv6 payload.
Next header—Previously the protocol field in IPv4, the Next Header field indicates the next extension header to examine.
Hop limit—Previously the time-to-live (TTL) field in IPv4, the hop limit indicates the maximum number of hops allowed.
Source address—Identifies the address of the source node sending the packet.
Destination address—Identifies the final destination node address for the packet.