BGP prefix filter list

Amir Herzberg amir.lists at
Sat May 18 17:08:07 UTC 2019

This discussion is very interesting, I didn't know about this problem, it
has implications to our work on routing security, thanks!

On Sat, May 18, 2019 at 11:37 AM Alejandro Acosta <
alejandroacostaalamo at> wrote:

>    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.

I wonder if this really is a consideration to avoid filtering small
prefixes (e.g. /24):

- attackers are quite likely to  do sub-prefix hijacks (or say a specific
/24), so I'm not sure this `hits' defenders more than it `hits' attackers
- I think we're talking only/mostly about small providers here, right? as
larger providers probably will not have such problems of tables exceeding
router resources.I expect such small providers normally connect thru
several tier-2 or so providers... if these upper-tier providers get
hijacked, the fact you've prevented this at the stub/multihome ISP may not
help much - we showed how this happens with ROV in our NDSS paper on it:

Amir Herzberg
Comcast professor for security innovation
Dept. of Computer Science and Engineering, University of Connecticut

Foundations of Cybersecurity:

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