Install Guide

The router redirect functionality in the neighbor discovery protocol (NDP) is similar to IPv4 router redirect messages. NDP uses
ICMPv6 redirect messages (Type 137) to inform nodes that a better router exists on the link.
IPv6 Headers
The IPv6 header has a fixed length of 40 bytes. This fixed length provides 16 bytes each for source and destination information
and 8 bytes for general header information.
The IPv6 header includes the following fields:
● Version (4 bits)
● Traffic Class (8 bits)
● Flow Label (20 bits)
● Payload Length (16 bits)
● Next Header (8 bits)
● Hop Limit (8 bits)
● Source Address (128 bits)
● Destination Address (128 bits)
IPv6 provides for extension headers. Extension headers are used only if necessary. There can be no extension headers, one
extension header or more than one extension header in an IPv6 packet. Extension headers are defined in the Next Header field
of the preceding IPv6 header.
Longest Prefix Match (LPM) Table and IPv6 /65 – /128 support
IPv6 Header Fields
The 40 bytes of the IPv6 header are ordered, as shown in the following illustration.
Figure 56. IPv6 Header Fields
Version (4 bits)
The Version field always contains the number 6, referring to the packet’s IP version.
Traffic Class (8 bits)
The Traffic Class field deals with any data that needs special handling. These bits define the packet priority and are defined
by the packet Source. Sending and forwarding routers use this field to identify different IPv6 classes and priorities. Routers
understand the priority settings and handle them appropriately during conditions of congestion.
Flow Label (20 bits)
The Flow Label field identifies packets requiring special treatment in order to manage real-time data traffic.
The sending router can label sequences of IPv6 packets so that forwarding routers can process packets within the same flow
without needing to reprocess each packet’s header separately.
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IPv6 Routing