Path Mtu Discovery; Ipv6 Neighbor Discovery - Dell S4048–ON Configuration Manual

S-series 10gbe switches

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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 Dell Networking OS ping and traceroute commands extend to support IPv6 addresses. These commands use ICMPv6

Type-2 messages.

Path MTU Discovery

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 59. Path MTU Discovery Process

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.

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.

IPv6 Routing