Max Prefix Out, was Re: Verizon 701 Route leak?

Jörg Kost jk at
Thu Aug 31 13:21:44 UTC 2017


but in reality you will factorise and summarize outbound and inbound 
numbers, create spare room for sessions and failover scenarios and 
therefore leaks and especially partial leaks can still occur.

In another example scenario the BGP process may not only shutdown the 
session to B, that has run into an outbound warning, but all other 
sessions to prevent "leaks". Last-resort the router will only judge by 
the number of the prefixes and therefore could shutdown himself by 
accident, especially if this router was not the origin. That could be a 
global headache ;-)


On 31 Aug 2017, at 13:06, Job Snijders wrote:

> Dear Jörg,
> On Thu, Aug 31, 2017 at 12:50:58PM +0200, Jörg Kost wrote:
>> but isn't peer A prefix-out a synonym for peer B prefix-in, that will
>> lead to the same result, e.g. a BGP teardown?
>> I just feel that this will add another factor, that people will not
>> use or abuse: neigh $x max-out infinite
> I feel you may be overlooking a key aspect here: Currently all of us
> rely on our peer's 'inbound maximum prefix limit', and obviously these
> are not always set correctly. An 'outbound maximum prefix limit' 
> offers
> networks that care about the rest of the world the option to
> 'self-destruct' the EBGP session in order to protect others.

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