See below... On Wed, 14 Feb 2001, Ryan O'Connell wrote:
On Tue, Feb 13, 2001 at 01:00:00PM -0800, Pyda Srisuresh wrote:
1. What is the maximum no. of peers a core-BGP peers with externally? What is a good average or median number? How does this vary with Tier-1 BGP speakers vs. Tier-2 BGP speakers? Also, What is an average no. of peers a BGP border router multi-homes with? (Do not include Border routers with a single ISP peer - only the multi-homed border routers)
I'm not sure what the maximum number supported by various OSes is, but most people seem to limit it to around 30-50 per router. Of course, the realisitic limit depends on router CPU and memory hardware more than anything else - a Cisco 3640 isn't going to be able to handle as much as a 12000GSR.
An "average" is meaningless - there are many rotuers out there that are multihomed to only two or three ISPs and therefore only have a handful of BGP sessions.
A GSR with 256MB will handle many full views. I haven't tested to the limits, but 50 would be a comfortable number. IOS based routers store additional views relatively efficiently. I'm sure someone with Cisco can give a better number, but from observation, if a full view take n memory, than each additional full view takes about .1n memory. On a Juniper, this relationship is much more linear. That's why most Junipers come with much more memory - 256mb will go south after a dozen full views. 768mb is recommended (and is what they ship with now, BTW).
2. I understand, an AS by itself does not originate more than 10,000 (UUnet being the one with this many) subnets. But, I believe, when you peer with a tier-1 ISP BGP speaker, you will get AS Paths for the entire 90,000+ routes (or whatever the maximum core routing tabel size is) exchanged at BGP connection setup time. On the other hand, I believe, the number of routes exchanged to be much less when you peer with a tier-2 BGP. What is a resonable average size of routing entries you could expect from a tier-2 ISP (and even a Tier-1 ISP, for that matter)?
Any ISP shuld give you the entire internet routing table - 90k+ prefixes. However, your router will only use a certain number of those as "best" routes. The number of "best" routes per ISP depends entirely on who the ISPs are, and doesn't (necessarily) have any relation to what Tier the ISPs are.
Routing policies (i.e. what you filter), have a much greater effect on routing table size as perceived by a downstream
3. Do yo have an estimate of memory requirements for some of the core routers (peering with tier-1 ISPs or tier-2 ISPs)? Is there a relation with the number of BGP peers?
A Cisco 3640 with 64Mb will (Or at least did) just about handle a BGP feed from two or three peers. Memory requirements (And CPU requirements) increase with the number of peers, but 192Mb should be plenty for most applications.
Not any more. We have had customer try this configuration and go to malloc hell. 128mb is the minimum for a full view these days. A Riverstone RS8000 or a Cisco 3640 will handle several full views nicely with 128mb. Remember the 3640 won't go above 128mb, though. A 3660 or a SSR makes a nice CPE box if you need 256mb.
-- Ryan O'Connell - <ryan@complicity.co.uk> - http://www.complicity.co.uk
I'm not losing my mind, no I'm not changing my lines, I'm just learning new things with the passage of time
Daniel Golding