Reference Guide

Path MTU Discovery
IPv6 path maximum transmission unit (MTU) discovery is supported on the S4820T platform.
Path 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 54. Path MTU Discovery Process
IPv6 Neighbor Discovery
IPv6 neighbor discovery protocol (NDP) is supported on the S4820T platform.
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.
NOTE: To avoid problems with network discovery, Dell Networking recommends configuring the static route last or
assigning an IPv6 address to the interface and assigning an address to the peer (the forwarding router’s address)
less than 10 seconds apart.
With ARP, each node broadcasts ARP requests on the entire link. This approach causes unnecessary processing by
uninterested nodes. With NDP, each node sends a request only to the intended destination via a multicast address with
the unicast address used as the last 24 bits. Other hosts on the link do not participate in the process, greatly increasing
network bandwidth efficiency.
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