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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: BGP deployment and peering questions
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 - <[email protected]> - 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
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