BGP Dampening

Two methods for reducing the impact of network instabilities are summarization and prefix dampening

Every time a prefix flaps, it is assigned an additive penalty value, 1000 by default. If this is just an attribute change, such as Local-Preference or AS_PATH, the penalty is halved, 500 by default. If the prefix becomes unavailable after flapping at least once, the BGP process still keeps it in the table, marked in “history” state to
account for further flaps and penalty accumulation. If the accumulated penalty value exceeds the Suppress Limit, which defaults to 2000, the BGP process will mark the route as damped

Half-Lifetime period, which specifies the amount of time needed to decrease the current penalty to the value twice smaller.
the decay process follows the equation P(t) = P(0)/2^(t/Half_Life), with the default Half_Lifetime of 15 minutes
As soon as the penalty falls below the Reuse Limit, the router will unsuppress the prefix and start advertising it again

R1#show run | s bgp
router bgp 123
 no synchronization
 bgp log-neighbor-changes
 bgp dampening 4 750 2000 10

Dampening with Route-Map
R1#
ip prefix-list DAMP seq 10 permit 5.5.5.0/24
!
route-map DAMPENING permit 10
 match ip address prefix-list DAMP
 set dampening 4 750 2000 10
!
router bgp 123
 no synchronization
 bgp log-neighbor-changes
 bgp dampening route-map DAMPENING