Juniper IGP - CONFIGURATION GUIDE V11.1.X, Configuration Manual

Page: 151 / 454

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 127.)
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.
IPv6 Overview
■ 127
Chapter 2: Configuring IPv6