Dampening
Dampening is a method used to limit the amount of network problems due to flapping routes. With dampening the flapping still occurs, but the peer routers pay less and less attention to that route as it flaps more often. One flap doesn’t start dampening, but the second starts a timer where the router will not use that route — it is considered unstable. If the route flaps again before the timer expires, the timer continues to increase. There is a period of time called the reachability half-life after which a route flap will only be suppressed for half the time. This half-life comes into effect when a route has been stable for a while but not long enough to clear all the dampening completely. For the flapping route to be included in the routing table again, the suppression time must expire.
If the route flapping was temporary, you can clear the flapping or dampening from the FortiGate units cache by using one of the execute router clear bgp commands:
execute router clear bgp dampening {<ip_address> | <ip/netmask>}
or
execute router clear bgp flap-statistics {<ip> | <ip/netmask>}
For example, to remove route flap dampening information for the 10.10.0.0/16 subnet, enter the command:
execute router clear bgp dampening 10.10.0.0/16
The BGP commands related to route dampening are:
config router bgp
set dampening {enable | disable}
set dampening-max-suppress-time <minutes_integer>
set dampening-reachability-half-life <minutes_integer>
set dampening-reuse <reuse_integer>
set dampening-route-map <routemap-name_str>
set dampening-suppress <limit_integer>
set dampening-unreachability-half-life <minutes_integer>
end