Re: BGP prefix filter list

[Blake Hudson <blake () ispn net>]

Radu-Adrian Feurdean wrote on 5/17/2019 5:10 AM:
> On Thu, May 16, 2019, at 16:38, Blake Hudson wrote:
> > offloading that responsibility onto the transit provider. IMHO, what's
> > the point of being multi-homed if you can't make intelligent routing
> > decisions and provide routing redundancy in the case of a transit
> > provider outage?
> Speaking of "intelligent routing", this is why doing some targeting on what you filter by some criteria other than 
> prefix or as-path length is a good idea. Either manually every once in a while (just make sure that you at least check the 
> situation every few weeks), or in an automated manner (better). You just need more data (usually *flow/ipfix based) in order to 
> be able to take the good decisions.
>
> You can use traffic levels (or better - lack of traffic), traffic criticality (?!?! cirticity ?!?!) and prefix count 
> saving as criteria.
>
> --
> R-A.F.

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 
only make the simplest of routing decisions; with dynamic default routes 
one can make more informed decisions; with a partial view of the 
internet one can make even better decisions; with a full view of the 
internet one can make good decisions; and with a routing protocol that 
takes into account bandwidth, latency, loss, or other metrics one can 
make the very best decisions.

Determining how intelligent one wants his or her decisions to be, and 
how much he or she is willing to spend to get there, is an exercise for 
the reader. Not all routers need a full view of the internet, but some 
do. The cost of routers that hold a full routing table in FIB is 
generally more than those that do not, but overall is not cost 
prohibitive (in my opinion) for the folks that are already paying to be 
multihomed. Single homed networks (or those with a single transit 
provider and additional peers), probably won't benefit from holding more 
than a default route to their transit provider and therefore may be able 
to get by with a less capable router. Each network is different and the 
choices driven by the needs for redundancy, availability, performance, 
and cost will come out differently as well.