Concept Guide

Generally, ICMPv6 uses two message types:
• Error reporting messages indicate when the forwarding or delivery of the packet failed at the destination or intermediate node. These
messages include Destination Unreachable, Packet Too Big, Time Exceeded and Parameter Problem messages.
• Informational messages provide diagnostic functions and additional host functions, such as Neighbor Discovery and Multicast Listener
Discovery. These messages also include Echo Request and Echo Reply messages.
The ping and traceroute commands extend to support IPv6 addresses. These commands use ICMPv6 Type-2 messages.
Path MTU Discovery
Dell Networking OS supports IPv6 path maximum transmission unit (MTU) discovery.
The size of the packet that can be sent across each hop in the network path without being fragmented is called the path maximum
transmission unit (PMTU). The PMTU value might dier for the same route between two devices, mainly over a public network, depending
on the network load and speed, and it is not a consistent value. The MTU size can also be dierent for various types of trac sent from
one host to the same endpoint. Path MTU discovery (PMTD) identies the path MTU value between the sender and the receiver, and uses
the determined value to transmit the packets across the network. Path MTU, in accordance with RFC 1981, denes the largest packet size
that can traverse a transmission path without suering fragmentation. Path MTU for IPv6 uses ICMPv6 Type-2 messages to discover the
largest MTU along the path from source to destination and avoid the need to fragment the packet. The recommended MTU for IPv6 is
1280. Greater MTU settings increase the processing eciency because each packet carries more data while protocol overheads (for
example, headers) or underlying per-packet delays remain xed.
Figure 59. Path MTU Discovery Process
IPv6 Neighbor Discovery
Dell Networking OS supports IPv6 neighbor discovery protocol (NDP).
NDP is a top-level protocol for neighbor discovery on an IPv6 network. In lieu of address resolution protocol (ARP), NDP uses “Neighbor
Solicitation” and “Neighbor Advertisement” ICMPv6 messages for determining relationships between neighboring nodes. Using these
messages, an IPv6 device learns the link-layer addresses for neighbors known to reside on attached links, quickly purging cached values
that become invalid.
NOTE
: If a neighboring node does not have an IPv6 address assigned, it must be manually pinged to allow the IPv6 device to
determine the relationship of the neighboring node.
IPv6 Routing 427