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Re: Number of BGP routes a large ISP sees in total
- From: Yi Wang
- Date: Tue Apr 17 23:14:48 2007
On Apr 17, 2007, at 10:22 PM, Patrick W. Gilmore wrote:
Exactly. Because this may be useful for traffic engineering.
On Apr 17, 2007, at 8:20 PM, Yi Wang wrote:
I guess what I see there is the lower bound of the path
diversity? Because even
though an edge router received more than one path for a prefix,
it'll only export
the best route to the other edge routers of the ISP.
Depends on the route server. If the route server has sessions with
lots of edges, it will have lots of prefixes. If not, then it's
generally got the same number of prefixes as you see in the CIDR
But you said: "if the RIB of all routers in the ISP were merged,
how many distinctive routes would there be?". Define
"distinctive"? Are you including things like same prefix & path,
but different next hop?
OK, let me try to put it this way:
If my guess is correct, the answer is "it varies". Some networks
have literally a dozen or more interconnection points. If the
networks are large, then you have 10s of 1000s of prefixes, with
dozens of next hops, and perhaps multiple that by multiple
networks. Then realize that many of the prefixes are duplicated
across multiple peers and ....
Anyway, the number is very difficult to determine. And it is
highly dependent on the network you look at.
Mind if I ask why you want to know? Perhaps there are some
simplifying assumptions we can make, depending upon your application?
If there was a single router (despite the scalability for a moment)
eBGP sessions with all the ISP's neighbors, how many routes (i.e.,
the "prefix, AS path,
next-hop" three-tuple) would it learn on average for each prefix?
I'm interested in the number of *raw* routes per prefix an ISP can
possibly learn, before any policy filters are applied. I know there
is no single number. Just want to have a rough
sense about the average (e.g., about 5? 10? 20?), as for a "large" ISP.
On Apr 17, 2007, at 8:02 PM, Ricardo V. Oliveira wrote:
Telnet to any of these route servers:
and do "show ip bgp"
On Apr 17, 2007, at 4:45 PM, Yi Wang wrote:
I should have said I'm interested in the merged size of RIB-In
(which contains all the raw
I couldn't find information about the number of different routes
for the same prefix
a (large) AS typically receives/learns. Hints?
On Apr 17, 2007, at 7:29 PM, Jeroen Massar wrote:
Yi Wang wrote:
Could anyone give me a sense how many BGP routes a large ISP
sees in total?
Here by "in total", I mean if the RIB of all routers in the
merged, how many distinctive
routes would there be?
Google(route bgp) "I am feelink lucky"
aka first hit, and just look around there.