North American Network Operators Group

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Re: BGP Path Filtering

  • From: Joe Abley
  • Date: Fri May 16 20:23:37 2003

On Friday, May 16, 2003, at 20:00 Canada/Eastern, Sean Donelan wrote:

Small ISPs with only a few eBGP neighbors (i.e. less than a dozen) and
a few network prefixes (i.e. less than a 100) probablly should stick with
hardcoded, explicit prefix and as-path filters. Coordinate the occasional
updates to the filters with your upstreams (since they should be
filtering your announcements on ingress anyway). You are less likely to
mess things up, and its simplier to understand if another network
engineer needs to debug things later.
Having being involved in cleaning up the networks of many small ISPs (by your definition of small) after they have been deployed by people long since departed, I completely disagree with your last sentence.

Maybe complexity is in the eye of the beholder, but ISPs which classify the routes they carry according to origin using community string attributes are much easier to debug and understand than those who specify their exit policy using hard-coded prefix and as-path filters all over the place.

I don't think "start messy and clean up later" is good advice. Do it right the first time, and grow smoothly without difficult migrations.


Joe