BGP prefix filter list

Tom Beecher beecher at
Wed May 15 19:20:42 UTC 2019

At a previous company , about 10-ish years ago, had the same problem due to
equipment limitations, and wasn't able to get dollars to upgrade anything.

The most effective thing for me at the time was to start dumping any prefix
with an as-path length longer than 10. For our business then, if you were
that 'far away' , there wasn't any good reason for us to keep your route.
Following default was going to be good enough.

It's still a reasonable solution I think in a lot of cases to filter out a
lot of the unnecessary prepend messes out there today.

On Wed, May 15, 2019 at 7:45 AM Baldur Norddahl <baldur.norddahl at>

> Hello
> This morning we apparently had a problem with our routers not handling
> the full table. So I am looking into culling the least useful prefixes
> from our tables. I can hardly be the first one to take on that kind of
> project, and I am wondering if there is a ready made prefix list or
> similar?
> Or maybe we have a list of worst offenders? I am looking for ASN that
> announces a lot of unnecessary /24 prefixes and which happens to be far
> away from us? I would filter those to something like /20 and then just
> have a default route to catch all.
> Thanks,
> Baldur
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