[nsp] BGP and Memory Requirements

From: Steve Lilley (slilley@thrupoint.net)
Date: Tue Sep 05 2000 - 07:10:20 EDT


Sorry about the cross-post to this list and the Cisco Spot list;
I only discovered this list yesterday! Anyway...I'm hoping that
someone with direct experience can provide some feedback!

1. The Internet routing tables are now approaching 88K routes.
   How much memory is required to handle this? I thought 64MB was
   still sufficient, but just last week I had a 4700M with 64MB of
   DRAM start bouncing once it reached about 82K routes (with a
   memory allocation failure). This repeated itself over and over
   again until the BGP session was shutdown.

   The million dollar question is: what is the minimum memory
   today for full routes? There's probably several answers to
   this question, depending on how close to the edge you want to
   run. Realizing that we'll hit 100K routes around the end of
   THIS year, I choose to be conservative! :-) The other aspect
   that confuses me in the amount of memory used for BGP in the
   output of the "show ip route summary" -- it usually shows
   something like 18MB, but I know the forwarding (FIB) table is
   close to 45MB, so this number doesn't make any sense.

2. When taking full routes from multiple sources on the same
   router (say two or three different providers), it is logical
   that this would require more memory, but it doesn't appear to
   require much more memory at all. I've got routers taking two
   Internet views, and they are using slightly more memory (about
   6MB) than those taking a single view. What's the deal?

3. Lastly, when applying BGP route filters (such as prefix
   filters) to incoming routes, aren't the filters applied as the
   routes are entered into memory? An example will help:
   shouldn't I be able to get away with MUCH less memory if I'm
   denying any routes larger than a /21 (i.e. permitting only
   /8 - /20, which gets the number of routes down to less than
   18K BGP routes). If this is true, theoretically I should be
   able to use a trusty 2500 router with with 16MB of DRAM and
   (massive) filtering to take the full routing table and filter
   it down. Is this accurate? (Not that *I* would ever do such
   a thing with a 2500, but perhaps someone else on this list
   has?)

Any feedback would be greatly appreciated!

Regards,
Steve Lilley
ThruPoint, Inc.



This archive was generated by hypermail 2b29 : Sun Aug 04 2002 - 04:12:16 EDT