Dampening

Scenario to verify BGP dampening parameter configuration.

By default, BGP processes all route updates immediately, including routes that frequently change state. When a route repeatedly appears and disappears, it consumes CPU resources and can cause network instability. Route-flap dampening addresses this problem by assigning penalties to unstable routes. When a route flaps, its penalty increases, and once the penalty exceeds a threshold, the route is marked as damped with the d flag and is no longer advertised to peers, even though it remains visible in the BGP table.

The dampening parameter requires four values that control the penalty system. The half-life determines how quickly penalties decay over time. The start-suppress-time sets the penalty threshold that triggers suppression. Once suppressed, a route remains damped until its penalty drops below re-use. The max-suppress-time caps how long any route can be suppressed regardless of its penalty.

In this test, DUT0 (AS 100) establishes an eBGP session with DUT1 (AS 200). The test configures aggressive dampening values to demonstrate the feature quickly. After simulating route flapping by repeatedly toggling redistribute connected, the route accumulates penalties and becomes suppressed, appearing with the d flag in the BGP table and in the dampening statistics. These aggressive values are optimized for testing; production environments typically use more conservative values to balance stability with responsiveness.

Test BGP Dampening

Description

This test verifies that route-flap dampening suppresses unstable routes by accumulating penalties. After configuring aggressive dampening values (1/1/1/1) on DUT0, the test simulates route flapping by repeatedly toggling redistribute connected on DUT1. The route quickly accumulates penalties and becomes suppressed, marked with the d (damped) flag in the BGP table. The test verifies the route appears in dampening statistics and is no longer advertised to peers until it stabilizes.

Scenario

Note

Enable dampening on DUT0 with aggressive values for fast testing (1/1/1/1). These values cause dampening to trigger quickly after just a few flaps. Production environments typically use more conservative values like 15/750/2000/60.

Step 1: Set the following configuration in DUT0 :

set interfaces ethernet eth0 address 10.10.0.100/24
set protocols bgp 100 neighbor peer remote-address 10.10.0.200
set protocols bgp 100 neighbor peer remote-as 200
set protocols bgp 100 neighbor peer route-map import PERMIT
set protocols bgp 100 parameters dampening half-life 1
set protocols bgp 100 parameters dampening max-suppress-time 1
set protocols bgp 100 parameters dampening re-use 1
set protocols bgp 100 parameters dampening start-suppress-time 1
set protocols route-map PERMIT rule 1 action permit
set system login user admin authentication encrypted-password '$6$GSjsCj8gHLv$/VcqU6FLi6CT2Oxn0MJQ2C2tqnRDrYKNF8HIYWJp68nvXvPdFccDsT04.WtigUONbKYrgKg8d6rEs8PjljMkH0'

Step 2: Set the following configuration in DUT1 :

set interfaces ethernet eth0 address 10.10.0.200/24
set protocols bgp 200 neighbor peer remote-address 10.10.0.100
set protocols bgp 200 neighbor peer remote-as 100
set protocols bgp 200 neighbor peer route-map export PERMIT
set protocols bgp 200 redistribute connected route-map PERMIT
set protocols route-map PERMIT rule 1 action permit
set system login user admin authentication encrypted-password '$6$GSjsCj8gHLv$/VcqU6FLi6CT2Oxn0MJQ2C2tqnRDrYKNF8HIYWJp68nvXvPdFccDsT04.WtigUONbKYrgKg8d6rEs8PjljMkH0'

Attention

Verify eBGP session establishes between DUT0 and DUT1.

Step 3: Run command protocols bgp show ip summary at DUT0 and check if output matches the following regular expressions:

10.10.0.200.*Established

Attention

Verify dampening parameters are configured correctly on DUT0.

Step 4: Run command protocols bgp show ip dampening parameters at DUT0 and check if output matches the following regular expressions:

Half-life time: 1 min[\s\S]+Reuse penalty: 1[\s\S]+Suppress penalty: 1[\s\S]+Max suppress time: 1 min

Attention

Verify DUT0 initially receives the connected network from DUT1.

Step 5: Run command protocols bgp show ip at DUT0 and check if output matches the following regular expressions:

[*](u|>).*10.10.0.0/24

Note

Simulate aggressive route flapping (5 times) with short intervals to accumulate penalties rapidly.

Attention

Verify route is now suppressed (damped) and appears in dampening statistics. The route accumulated penalties from flapping and exceeded the start-suppress-time threshold.

Step 6: Run command protocols bgp show ip dampening dampened-paths at DUT0 and check if output matches the following regular expressions:

d.+10.10.0.0/24

Attention

Verify route appears with damped flag *d in BGP table. The asterisk indicates the route is valid, and the d flag shows it is damped and not being advertised.

Step 7: Run command protocols bgp show ip at DUT0 and check if output matches the following regular expressions:

d.+10.10.0.0/24