BGP Attack - Best Defense ?

Steve Gibbard scg at gibbard.org
Fri Aug 29 17:50:49 CDT 2008


On Fri, 29 Aug 2008, Scott Weeks wrote:

> I am signed up for the Prefix Hijack Alert System 
> (phas.netsec.colostate.edu) and would be alerted in about 6 hours (or 
> less?) about a prefix announcement change.
>
> I then would deaggregate (as little as possible) to be able to announce 
> the same more specific as the attacker.

Announcing the same prefix length as the attacker would get you back some 
portion of your traffic, rather than all of it.  You'd really want to 
announce something more specific than what the attacker is announcing.

Of course, then you'd need to get your upstreams to accept the more 
specific, which might mean modifying filters.  How quickly can you get 
your upstreams to do that?

Also, please don't be like Covad.  If you deaggregate to deal with a 
highjacking, make your deaggregation temporary, and clean it up when it's 
not needed anymore.

> I would then try to contact the ASs still using the attack path to get 
> it stopped.  (Yell help on NANOG? ;-)

If you try to contact networks that are innocently hearing the 
announcement, rather than those involved in propagating it, you'll have a 
lot of networks to contact.  A better move would be to contact those 
originating the announcement (unless you think they're involved in 
something malicious), and then their upstreams, and if that doesn't work, 
their upstreams' upstreams.

Calling an upstream provider's NOC to ask them to modify a customer's 
filters generally gets met with lots of skepticism.  You'll almost 
certainly be told that you have to be the customer whose filter it is to 
ask to have it modified.  You'll need to be quite firm, and will probably 
need to ask to speak to somebody higher up than the front-line tech who 
answers the phone.  The very few times I've had to do this, I've also 
found it quite useful to deemphasize their receiving of the prefix from a 
customer, and emphasize that they were announcing it to the rest of the 
world.  "You are announcing our prefix, and you are not authorized to do 
so," is a useful line.

-Steve




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