Users Guide

Path MTU Discovery
Path MTU (Maximum Transmission Unit) 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 59. Path MTU Discovery Process
IPv6 Neighbor Discovery
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 547