Reference Guide

408 | IPv6 Routing
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Neighbor Discovery Protocol (NDP) is a top-level protocol for neighbor discovery on an IPv6 network. In
lieu of 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.
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.
Figure 19-3. NDP Router Redirect
IPv6 Neighbor Discovery of MTU packets
With FTOS 8.3.1.0, you can set the MTU advertised through the RA packets to incoming routers, without
altering the actual MTU setting on the interface. The
ipv6 nd mtu command sets the value advertised to
routers. It does not set the actual MTU rate. For example, if
ipv6 nd mtu is set to 1280, the interface will still
pass 1500-byte packets, if that is what is set with the
mtu command.
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 Force10 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.
Network 2001:db8::1428:57abNetwork 2001:db8::1428:57ab
Router C
Router A
Router B
Send a Packet to
Network 2001:db8::1428:57ab
Local Link
Packet Destination (2001:db8::1428:57ab)
ICMPv6 Redirect (Data: Use Router C)
Packet Destination (Destination 2001:db8::1428:57ab)