IPv6 packet headers contain many of the fields found in IPv4 packet headers; some of these fields differ from IPv4.
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.
- Flow label – The flow label identifies all packets belonging to a specific flow (that is, packet flows requiring a specific class of service
- 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.
In IPv6, optional extension headers are used to encode optional Internet-layer information. Extension headers are placed between the IPv6 header and the upper-layer header in a packet. Multiple extension headers can be chained together using the next header field. The next header field, located in the IPv6 header, indicates to the router which extension header to expect next. If there are no more extension headers, the next header field indicates the upper-layer header (such as TCP header, UDP header).
Today we covered an Introduction to IPv6 in which we learned the basic purpose behind the move to IPv6 and what features IPv6 provides and also the format and brief description of the IPv6 Packet format. In the upcoming lessons we will delve more into IPv6 covering the addressing architecture and transition mechanisms.