IP event dampening is a feature to provide for a generic interface dampening mechanism. This mechanism provides a configurable exponential decay mechanism very similar to BGP dampening that can be used to suppress excessive interface flapping events on routing protocols and routing tables in the network. Dampening an interface effectively removes it from the network until the interface is stable and stops flapping (bouncing up and down). Configuring IP event dampening also improves stability and convergence time, because these disturbances are not propagated to other parts of the network, thus reducing the wastage of system resources required to process them.
The only problem with this feature is that it can be configured only on an interface, and all subinterfaces will inherit this feature. You cannot configure this feature on selective subinterfaces.
When configured, flapping interfaces are identified, assigned penalties, and suppressed if necessary. This means that as far as the supported routing protocols and HSRP are concerned, the interface is considered to be down, and connected routes for the suppressed interface are removed from the routing table.
Configuring IP Event Dampening
R1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#interface serial 2/0
R1(config-if)#dampening [half-life reuse-threshold suppress-threshold max-suppress
restart-penalty]
R1(config-if)#^Z
R1#
Output of debug dampening interface
R1#debug dampening interface
interface debugging is on
*Jun 30 08:07:13.207: IF-EvD(Ethernet0/0): IP Routing reports state transition from UP to DOWN
*Jun 30 08:07:13.207: IF-EvD(Ethernet0/0): setting merged state from UP to DOWN
*Jun 30 08:07:13.207: EvD(Ethernet0/0): charge penalty 1000, new accum. penalty
1000, flap count 1
*Jun 30 08:07:13.207: EvD(Ethernet0/0): accum. penalty 1000, not suppressed
*Jun 30 08:07:13.207: IF-EvD(Ethernet0/0): update IP Routing state to DOWN,
interface is not suppressed
!Output omitted for brevity
*Jun 30 08:07:16.899: EvD(Ethernet0/0): accum. penalty decayed to 1529 after 1 second(s)
*Jun 30 08:07:16.899: EvD(Ethernet0/0): charge penalty 1000, new accum. penalty 2529, flap count 3
*Jun 30 08:07:16.899: EvD(Ethernet0/0): accum. penalty 2529, now suppressed with a reuse intervals of7
!Output omitted for brevity
*Jun 30 08:07:33.911: EvD(Ethernet0/0): accum. penalty decayed to 968 after 10 second(s)
*Jun 30 08:07:33.911: EvD(Ethernet0/0): accum. penalty 968, now unsuppressed
*Jun 30 08:07:33.911: IF-EvD(Ethernet0/0): update IP Routing state to UP, interface is not suppressed
*Jun 30 08:07:41.667: IF-EvD(Ethernet0/0): IP Routing reports state transition from UP to UP
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