WB1 7.53 BGP Dampening with Route-Map

7.53 BGP Dampening with Route-Map

• Ensure that dampening process applies only to AS 100 originated routes, and does not affect any other prefixes.

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Sometimes it might be desirable to apply dampening only to a certain set of routes, e.g. to the prefixes originated from the “problematic” AS. Another good example might be a set of prefixes describing critical network resources that must always be available.

To account for such situations it is possible to use a route map with the BGP dampening command to select prefixes eligible for
dampening. The command

bgp dampening route-map <MAP_NAME>

where the route-map may match IP addresses using access-lists, prefix-lists and as-path lists. For every route-map entry you may set specific dampening parameters using the command

set dampening <Half_Life> <ReuseLimit> <SuppressLimit> <MaximumSuppressTime>.

For this task, we create an AS_PATH access-list matching the paths originated in AS 100 and set the dampening parameters using the Half-Life value of 4 minutes.

R2, R3, R5, SW2, SW4:
ip as-path access-list 100 permit _100$
!
route-map DAMPENING
 match as-path 100
 set dampening 4 750 2000 16
!
router bgp 200
 no bgp dampening
 bgp dampening route-map DAMPENING

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Configure R3 for BGP dampening debugging. Next, configure SW1 for minimal advertisement interval and do a number of consecutive shutdowns/no shutdowns for Loopback1 interface. After this, go to R1 and perform the same series of operations on Loopback1.

Rack1SW1#config t
Enter configuration commands, one per line.  End with CNTL/Z.
Rack1SW1(config)#router bgp 65089
Rack1SW1(config-router)#neighbor 155.1.37.3 advertisement-interval 0
Rack1SW1(config-router)#

Rack1R3#debug ip bgp dampening
BGP dampening debugging is on for address family: IPv4 Unicast

Now check BGP dampening settings in R3. Notice that the dampening settings only apply to the prefixes matching the route map. Next, check the output for the debugging command activated above. Notice that the only prefix tracked by the dampening process is 1.1.1.0/24.

Rack1R3# show ip bgp dampening parameters
 dampening 4 750 2000 16 (route-map DAMPENING 10)
  Half-life time      : 4  mins       Decay Time       : 620 secs
  Max suppress penalty: 12000         Max suppress time: 16 mins
  Suppress penalty    :  2000         Reuse penalty    : 750
Rack1R3#