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Copyright © 2010, Juniper Networks, Inc.
Figure 13: IPv4 and IPv6 Header Comparison
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 on page 123.)
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.
Extension Headers
In IPv6, 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.
Chapter 2: Configuring IPv6
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