BGP prefix filter list

Alejandro Acosta alejandroacostaalamo at
Sat May 18 15:35:39 UTC 2019


    As a comment, after receiving several complains and after looking 
many cases, we evaluated what is better, to cut the table size filtering 
"big" network or "small" networks.  Of course this is a difficult 
scenario and I guess there are mix thinking about this, however, we 
concluded that the people (networks) that is less affected are those who 
learn small network prefixes (such as /24, /23, /22, /21 in the v4 world).

   If you learn, let's say, up to /22 (v4), and someone hijacks one /21 
you will learn the legitimate prefix and the hijacked prefix. Now, the 
owner of the legitimate prefix wants to defends their routes announcing 
/23 or /24, of course those prefixes won't be learnt if they are filtered.

   We published this some time ago (sorry, in Spanish):

That's it, my two cents.


On 5/15/19 7:43 AM, Baldur Norddahl wrote:
> 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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