Re: Talked about this before

[Iljitsch van Beijnum <iljitsch () muada com>]

On Mon, 9 Sep 2002, Pawlukiewicz Jane wrote:

> Quick Question, how much memory does the bgp tables actually take. I'm
> estimating 32 mb in my plan, but I'm worried that's not enough.

Probably not. I assume you're talking about Cisco? I've done some
calculations under different circumstances, but the results vary. I think
the IOS version and CPU architecture have something to do with that. And
then there's stuff like average AS path length and how many other
attributes, such as communities, routes tend to have. Quick rule of thumb:
about 300 bytes per BGP route, where each route from each peer counts
seperately.

Don't forget you also need a routing table, which uses about the same
(maybe slightly less) per entry, but there is only one entry in the
routing table per destination prefix (unless you do load balancing).
Finally, you're probably running CEF so that's another several hundred
bytes per destination (this one seems to vary the most).

A quick guestimate would be:

    (# full BGP views + 2) * global routing table size * 300 bytes

I tried to figure out the numbers for Zebra just the other day, and they
were surprisingly similar.