Users Guide

Layer 3 Routing Commands 1601
When NUD is triggered, neighbor solicitation PROBE packets (unicast and
multicast) are sent periodically, separated by exponential binary values
instead of the normal 1 second interval. This ensures that when the network
(not just our router but more routers in the network) is congested, the NUD
process for the existing STALE entries takes enough time before ultimately
removing the cache entry through garbage collection. Without the
exponential backoff timing for retransmissions, there is a higher probability
that the cache entry is removed resulting in the disruption of the existing
traffic.
Another significant benefit of delayed neighbor solicitation retransmission is
higher robustness against transient failures, such as spanning tree re-
convergence and other layer 2 issues that can take many seconds to resolve.
The exponential back-off calculation is
next retransmission timer =
(BACKOFF_MULTIPLE^solicit_attempt_num) *$RETRANS_TIMER +
jittered value.
The exponential backoff algorithm complies with draft-ietf-6man-impatient-
nud-02.
Increase this value when large numbers of neighbors are present or when
neighbors are not being discovered due to network events like spanning-tree
re-convergence.
Command History
Introduced in version 6.2.0.1 firmware.
Example
console (config)#ipv6 nd nud retry 5
ipv6 nd other-config-flag
Use the ipv6 nd other-config-flag command in Interface Configuration mode
to set the “other stateful configuration” flag in router advertisements sent
from the interface.
Syntax
ipv6 nd other-config-flag