BGP deployment and peering questions
Daniel L. Golding
dan at netrail.net
Wed Feb 14 16:00:55 UTC 2001
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 at 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
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