Router 2

Router 1 is configured by:

• Configuring the flap1 flap table on Router 2 with:
  • cutoff set to 150
  • reuse set to 75
  • hold-time set to 300
• Applying the flap1 flap table to the map1 BGP route-map
• Configuring Router 2 with a BGP neighbor 192.168.12.111 (AS 10)
• Applying the map1 inbound route-map to neighbor 192.168.12.111
• Clear the BGP session to initiate a readvertisement of the route from Router 1 to Router 2
• Display the route and route flap dampening details

  System(su)->configure
  System(su-config)->dampen-flap flap1
  S Chassis(su-config-dampen-flap)->cutoff 150
  S Chassis(su-config-dampen-flap)->reuse 75
  S Chassis(su-config-dampen-flap)->hold-time 300
  S Chassis(su-config-dampen-flap)->exit
  System(su-config)->route-map bgp map1 permit 10
  System(su-config-route-map-bgp)->set flap-table flap1
  System(su-config-route-map-bgp)->exit
  S Chassis(su-config)->router bgp 5
  System(su-config-bgp)->bgp router-id 2.3.4.5
  System(su-config-bgp)->neighbor 192.168.12.111 remote-as 10
  System(su-config-bgp)->neighbor 192.168.12.111 route-map map1 in
  System(su-config-bgp)->exit
  System(su-config)->

The following displays route dampening statistics for network 1.0.0.0/8 prior to any instability:

System(su-config)->show ip bgp 1.0.0.0/8 detail
Route status codes: > - active
    Network                  Next Hop              Rib MED Local-Pref Origin AS Path
>   1.0.0.0/8                192.168.12.111        U   0      100    Inc     10
Community attributes in route:
Extended Community attributes in route:
Route Flap Dampening configuration file name: flap1
Is route suppressed? No
Flap penalty: 0, Flap Count 0, Flap time remaining 0 seconds
System(su-config)->

If you were to enter the show command immediately after the first flap, the route flap dampening statistics would show:

System(su-config)->show ip bgp 1.0.0.0/8 detail
Route status codes: > - active
...
Route Flap Dampening configuration file name: flap1
Is route suppressed? No
Flap penalty: 99, Flap Count 1, Flap time remaining 0 seconds

The route remains unsuppressed because the route penalty has not exceeded the cutoff value. The flap penalty has decayed by 1 point from 100 to 99 since the route flap occurred. The flap count is 1 and because the route has not yet been suppressed, flap time is set to 0 seconds.

Entering the show command immediately after the second route flap, the route flap dampening statistics would show:

System(su-config)->show ip bgp 1.0.0.0/8 detail
Route status codes: > - active
...
Route Flap Dampening configuration file name: flap1
Is route suppressed? Yes
Flap penalty: 185, Flap Count 2, Flap time remaining 295 seconds

Because the flap penalty exceeds the cutoff setting, route flap dampening has suppressed the route. Flap time now displays the amount of seconds remaining before the hold-time is reached.

After waiting the 5 minute hold-time, the display shows that the route has been unsuppressed. If the hold-time was set to the default value of 900 seconds, and no other router flaps occurred for this route, the route penalty would have decayed to the point that the route would have been unsuppressed when the route penalty reached the reuse setting of 75.

System(su-config)->show ip bgp 1.0.0.0/8 detail
Route status codes: > - active
...
Route Flap Dampening configuration file name: flap1
Is route suppressed? No
Flap penalty: 86, Flap Count 2, Flap time remaining 0 seconds

Configuring BGP Flap Dampening describes how to configure the BGP flap dampening.