BGP Peering and Prefix filterin Question


Recently I have been told that some ISP’s are automatically or maybe manually modifying their BGP inbound prefix listing after a network is not advertised to them for a period of time.

So the questions I pose to the group:

  1. Is this normal?

  2. Can anyone share your policies?

  3. Who does it?

  4. How often?

  5. Is it automagic? Or the dirty work slaved off to the junior engineer in the corner somewhere?

a. I know you probably won’t trust that junior engineer, but some do….

Anyway just a little research after a small problem a customer recently had.



hi there…

Who would have the time to monitor this if it was a manual process? :wink:

Personally, never heard of that but it may happen out there…

We use strict RADB filtering on 95% of our connections. Once a day, we run a copy of IRRPT against a list of peered AS’s and update the prefix-lists

For transit, we just sanitize the routes (drop private space, drop small subnets etc.)

Take care,


I’m suspecting that the customers problem was BGP Flap Damping (or Dampening) and that somehow the explanation got lost in translation somewhere (I’ve tried explaining it to some non-engineers sometimes and it is a tricky concept for many to grasp for some reason…)

Whether its “normal” or a good idea or who does / doesn’t do it is a topic fraught with religion…



You are correct on the translation—

Finally heard back from all players.

And someone “properly” summarized the prefixes.

Initially they were sent as 4 /24’s due to data center disparity and a route policy.

But in the end someone at the 1st upstream summarized the routes to their upstreams.

And when the 1st upstream realized they should not be summarizing and changed that- their upstreams blocked the traffic.

Go figure…

Thanks for the input guys!