Header Structure; Extension Headers; Ipv6 Addressing - Juniper ACX1000 Configuration Manual

IPv6 Addressing

Copyright © 2017, Juniper Networks, Inc.

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 class of service. 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 IP.

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.
Extension headers are chained together using the next header field in the IPv6 header.
The next header field 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 (TCP header, User Datagram Protocol [UDP] header, ICMPv6 header, an
encapsulated IP packet, or other items).
IPv6 uses a 128-bit addressing model. This creates a much larger address space than
IPv4 addresses, which are made up of 32 bits. IPv6 addresses also contain a scope field
that categorizes what types of applications are suitable for the address. IPv6 does not
support broadcast addresses, but instead uses multicast addresses to serve this role. In
addition, IPv6 also defines a new type of address called anycast.
NOTE: You cannot configure a subnet zero IPv6 address because RFC 2461
reserves the subnet-zero address for anycast addresses, and Junos OS
complies with the RFC.
Chapter 18: Configuring Routing Protocols
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