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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.
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