Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 476
ICMPv6, Path MTU Discovery, IPv6 Neighbor Discovery
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ICMPv6 ICMP for IPv6 (ICMPv6) combines the roles of ICMP, IGMP and ARP in IPv4. Like IPv4, it provides functions for reporting delivery and forwarding errors, and provides a simple echo service for troubleshooting. The implementation of ICMPv6 is based on RFC 4443. 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 IPv6 path maximum transmission unit (MTU), in accordance with RFC 1981, defines the largest packet size that can traverse a transmission path without suffering 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 processing efficiency because each packet carries more data while protocol overheads (for example, headers) or underlying per-packet delays remain fixed. Figure 55. Path MTU Discovery Process IPv6 Neighbor Discovery The IPv6 neighbor discovery protocol (NDP) is a top-level protocol for neighbor discovery on an IPv6 network. In place 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 476
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