[ppml] Effects of explosive routing table growth on ISP behavior

Scott Leibrand sleibrand at internap.com
Wed Oct 31 18:46:43 EDT 2007

Jason Schiller wrote:
> On Wed, 31 Oct 2007, Scott Leibrand wrote:
>>> For large ISPs with widespread peeing, and lots of mult-homed customer
>>> overlap, this basiclly means they need to carry nearly all of the routes.
>> Perhaps you could help us understand the magnitude of the difference a 
>> little better with some actual statistics, if you could share them.  Of 
>> the /23 and /24 routes in your table (excluding class C swamp space), 
>> how many (and what percentage) are non-customer routes?  My intuition / 
>> hypothesis would be that the non-customer routes outnumber the customer 
>> routes, so you would still get significant benefit from filtering the 
>> non-customer more-specifics if we come to a routing-table-size crunch.
> I am not authorized to share specific numbers.
Fair enough.

> If my customers want shortest path forwarding (as determined by BGP path 
> selection) to destinations on the Internet than I need to carry are the
> multi-homed more specifics of all of my direct Peers.  That will not
> reduce my tables by much.

Yes, and today you and your customers value shortest path forwarding 
more than a smaller BGP table, with good reason.  However, if the BGP 
table were to grow, wouldn't it be better for you and your customers to 
relax the requirement for shortest path forwarding rather than drop 
reachability altogether?  While my customers might complain once in a 
while that their traceroute goes through a few extra hops and adds a few 
ms of latency, they get extremely upset if they lose reachability to a 
destination entirely.


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