Internet routing table and damping on JunOS

To get an idea about the current number of Internet routes, for both IPv4 and IPv6:

moghaddas@USA> show route summary | match "inet|bgp"  
inet.0: 560133 destinations, 1663174 routes (558798 active, 0 holddown, 1525 hidden)
                 BGP: 1663124 routes, 558752 active
inet6.0: 24047 destinations, 47458 routes (23459 active, 0 holddown, 851 hidden)
                 BGP:  47444 routes,  23447 active

Now, imagine what would be the outcome of route flaps for a Service Provider environment with many eBGP neighbors. Instability and customer dissatisfaction!

The first solution to avoid such situations is BGP Route Dampening/Damping.

RIPE-580 says:

Route Flap Damping (RFD) [1] is a mechanism for BGP speaking routers that penalises prefixes that exhibit a large number of updates (‘flapping’), and suppresses a route when the accumulated penalty exceeds a given threshold.  The penalty decays over time until it reaches a lower threshold at which point the route is unsuppressed. RFD is intended to improve the overall stability of the Internet routing table and reduce the load on BGP speaking routers.

Piece of cake, yeah? Then let’s dive into a sample configuration for JunOS.

  1. I created the damping policy, named AGGRESSIVE, based on RFC7196 and RIPE-580, which is not really conservative, but little bit destructive and somewhat aggressive:

    I assume that you know what each parameter does, otherwise I’m sure you will google it!

  2. Then, the damping policy should be referenced in an import policy:
  3. Now, in BGP configuration, after adding the import policy globally, or for a specific neighbor/group, BGP damping should be enabled, which can also be done globally or for a specific neighbor/group:

Let’s verify.

  • Which routes have flapped (decayed) and might become damped (suppressed)
  • Which routes are suppressed (damped)
  • Which routes are withdrawn but have history
  • You want more information? Then try the “extensive” switch!
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Author: Mo Moghaddas

Building to give users more time back and make scheduling a pleasant experience.

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