Re: BGP prefix filter list

["Radu-Adrian Feurdean" <nanog () radu-adrian feurdean net>]

On Fri, May 17, 2019, at 15:28, Blake Hudson wrote:

>  From my perspective one's ability to intelligently route IP traffic is 
> directly correlated to the data they have available (their routing 
> protocol and table). For example, with static default routes one can 

For me, routing table and available routing protocols are not the only things needed for intelligent routing. And the 
router is not the only component involved in "intelligent routing". Not these days/not anymore.

One thing that can help immensely in an internet environment is knowing where the data goes and where it comes from. 
Knowing your "important" traffic source/destinations is part of it.

You can say "I can no longer keep all the routes in FIB, so I'll drop the /24s", then come to a conclusion that that 
you have loads of traffic towards an anycast node located in a /24 or that you exchange voice with a VoIP provider that 
announces /24. you just lost the ability to do something proper with your important destination. On the other hand, you 
may easily leave via default (in extreme cases even drop) traffic to several /16s from Mulgazanzar Telecom which which 
you barely exchange a few packets per day except the quarterly wave of DDoS/spam/scans/[name your favorite abuse]. Or 
you may just drop a few hundred more-specific routes for a destination that you do care about, but you cannot do much 
because network-wise it is too far away.

Of course, such an approach involves human intervention, either for selecting the important and non-important 
destinations or for writing the code that does it automagically. Or both. There is no magic potion. (as a friday 
afternoon remark, there used to be such a potion in France, the "green powder", but they permanently ran out of stock 
in 2004 - see http://poudreverte.org/ - site in fr_FR).