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Header Structure
IPv6 packet headers contain many of the fields
found in IPv4 packet headers; some of these fields have been modified
from IPv4. The 40-byte IPv6 header consists of the following 8 fields:
- Traffic class—Class-of-service (CoS) priority of
the packet. Previously the type-of-service (ToS) field in IPv4. However,
the semantics of this field (for example, DiffServ code points) are
identical to IPv4.
- Destination address—Final destination node address
for the packet.
- Flow label—Packet flows requiring a specific CoS.
The flow label identifies all packets belonging to a specific flow,
and routers can identify these packets and handle them in a similar
fashion.
- Hop limit—Maximum number of hops allowed. Previously
the time-to-live (TTL) field in IPv4.
- Next header—Next extension header to examine. Previously
the protocol field in IPv4.
- Payload length—Length of the IPv6 payload. Previously
the total length field in IPv4.
- Source address—Address of the source node sending
the packet.
- Version—Version of the Internet Protocol.
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