BGP prefix filter list

Robert Blayzor rblayzor.bulk at
Thu May 30 21:28:57 UTC 2019

On 5/30/19 1:48 PM, William Herrin wrote:
> 1. What happens to the packets when the /24 gets filtered from one
> source (in favor of an aggregate) but not from the other? 
> 2. In exchange for this liability, did you gain any capacity in your router?

It was my understanding that the argument for filtering at your own
edge, routes which you receive that has an aggregate covering route and
a /24 more specific prefix.

For a single multi-homed network with two transit ISP's it won't make
much of a difference unless you are strapped for outbound bandwidth.
Filter away, because you have a covering aggregate route.

I'm not saying this will work for ALL networks of any size, but for
organizations with just a couple of transit links and not much TE going
on, it would be a perfectly viable option rather than overloading your
TCAM due to budget constraints...


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