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JUNOS Cookbook by Aviva Garrett

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13.12. Mitigating Route Instabilities with Route Flap Damping

Problem

You want to deal with potential route instabilities caused by routes being withdrawn in a series of BGP Update messages only to be readvertised as active routes a few minutes later when an intermittently failing link is restored.

Solution

Route flap damping is a way to prevent flapping routes from destabilizing BGP. In the JUNOS software, you set up damping by using routing policy. There are four steps in setting up damping:

  1. Define the damping parameters:

    	[edit policy-options]
    	aviva@Router3# set damping damping-normal suppress 6000
    	aviva@Router3# set damping standard-damping half-life 15
    	aviva@Router3# set damping standard-damping reuse 3000
    	aviva@Router3# set damping standard-damping max-suppress 30
  2. Create a routing policy that references the damping parameters:

    	[edit policy-options]
    	aviva@Router3# set policy-statement damping-policy from route-filter 10.0.31.1/32
    	exact
    	aviva@Router3# set policy-statement damping-policy then damping damping-normal
    	aviva@Router3# set policy-statement damping-policy then accept
  3. Enable route flap damping for BGP:

    	[edit protocols bgp]
    	aviva@Router3# damping
  4. Apply the damping policy to a BGP group:

    	[edit protocols bgp]
    	aviva@Router3# set group session-to-AS65505 import damping-policy

Discussion

If a link on the network is intermittently failing, routes can be withdrawn and readvertised in quick succession as the link goes down and then comes back up. This route flapping forces BGP to change ...

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