Neighbor Discovery

IPv6 nodes (routers and hosts) on the same link use neighbor discovery (ND) to discover link-layer addresses and to obtain and advertise various network parameters and reachability information. ND combines the services for IPv4 with the Address Resolution Protocol (ARP) and router discovery. In IPv6 ND performs a function similar to ARP (Address Resolution Protocol) in IPv4.

Hosts use ND to discover the routers in the network that you can use as the default routers, and to determine the link-layer address of neighbors attached to local links. Routers also use ND to discover neighbors and link-layer information. ND updates the neighbor database with valid entries, invalid entries, and entries migrated to various locations.

The ND protocol provides the following services:

Neighbor discovery uses three components:

Note

Note

When a neighbor transitions to the STALE state, to initiate Neighbor Unreachability detection (NUD), a duplicate copy of the traffic destined to this neighbor is sent to the switch Control Processor (CP) on a low priority queue (queue 0). The original packet is forwarded to this neighbor. After NUD is initiated, the hardware records are updated and the traffic is no longer sent to the CP. When a high rate of such traffic is sent to the CP, the switch can drop some of these packets due to the built-in CP rate limiting feature, which protects the CP from DOS attacks.

Use the command show qos cosq-stats cpu-port to view drop statistics on the CPU queue. This design does not result in loss of traffic.

Use the command ipv6 nd reachable-time <0-3600000> to increase the default value of 3000 milliseconds, which in turn delays the scenario of data path sending STALE neighbor destined packets to the CP.

As a best practice, configure a reachable time value of 180000 and retransmit interval of 5000.