Administrator Guide

Table Of Contents
Link Dampening
Interface state changes occur when interfaces are administratively brought up or down or if an interface state changes.
Every time an interface changes a state or flaps, routing protocols are notified of the status of the routes that are affected by
the change in state. These protocols go through the momentous task of re-converging. Flapping; therefore, puts the status of
entire network at risk of transient loops and black holes.
Link dampening minimizes the risk created by flapping by imposing a penalty for each interface flap and decaying the penalty
exponentially. After the penalty exceeds a certain threshold, the interface is put in an Error-Disabled state and for all practical
purposes of routing, the interface is deemed to be down. After the interface becomes stable and the penalty decays below a
certain threshold, the interface comes up again and the routing protocols re-converge.
Link dampening:
reduces processing on the CPUs by reducing excessive interface flapping.
improves network stability by penalizing misbehaving interfaces and redirecting traffic.
improves convergence times and stability throughout the network by isolating failures so that disturbances are not
propagated.
Important Points to Remember
Link dampening is not supported on VLAN interfaces.
Link dampening is disabled when the interface is configured for port monitoring.
You can apply link dampening to Layer 2 and Layer 3 interfaces.
You can configure link dampening on individual interfaces in a LAG.
Enabling Link Dampening
To enable link dampening, use the following command.
Enable link dampening.
INTERFACE mode
dampening
To view the link dampening configuration on an interface, use the show config command.
R1(conf-if-te-1/1)#show config
!
interface TenGigabitEthernet 1/1
ip address 10.10.19.1/24
dampening 1 2 3 4
no shutdown
To view dampening information on all or specific dampened interfaces, use the show interfaces dampening command
from EXEC Privilege mode.
Dell# show interfaces dampening
InterfaceStateFlapsPenaltyHalf-LifeReuseSuppressMax-Sup
Te 1/1Up005750250020
Te 1/2Up21200205001500300
Te 1/2Down4850306002000120
To view a dampening summary for the entire system, use the show interfaces dampening summary command from
EXEC Privilege mode.
Dell# show interfaces dampening summary
20 interfaces are configured with dampening. 3 interfaces are currently suppressed.
Following interfaces are currently suppressed:
Te 1/2
Te 3/1
Te 4/2
Dell#
Interfaces
287