[96127] in North American Network Operators' Group
Re: Number of BGP routes a large ISP sees in total
daemon@ATHENA.MIT.EDU (Yi Wang)
Tue Apr 17 23:13:43 2007
In-Reply-To: <BDD6A3EA-7968-4363-8474-A65535CAE2B2@ianai.net>
Cc: Yi Wang <yiwang@CS.Princeton.EDU>, nanog@merit.edu
From: Yi Wang <yiwang@CS.Princeton.EDU>
Date: Tue, 17 Apr 2007 23:11:56 -0400
To: "Patrick W. Gilmore" <patrick@ianai.net>
Errors-To: owner-nanog@merit.edu
Hi Patrick,
On Apr 17, 2007, at 10:22 PM, Patrick W. Gilmore wrote:
>
> 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
> report.
>
> 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?
Exactly. Because this may be useful for traffic engineering.
>
> 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?
OK, let me try to put it this way:
If there was a single router (despite the scalability for a moment)
that maintains
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.
Thanks,
Yi
>
> --
> TTFN,
> patrick
>
>
>> On Apr 17, 2007, at 8:02 PM, Ricardo V. Oliveira wrote:
>>
>>>
>>> Telnet to any of these route servers:
>>> http://www.bgp4.net/wiki/doku.php?id=tools:ipv4_route_servers
>>>
>>> and do "show ip bgp"
>>>
>>> --Ricardo
>>>
>>> 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
>>>> routes received).
>>>>
>>>> I couldn't find information about the number of different routes
>>>> for the same prefix
>>>> a (large) AS typically receives/learns. Hints?
>>>>
>>>> Yi
>>>>
>>>> On Apr 17, 2007, at 7:29 PM, Jeroen Massar wrote:
>>>>
>>>>> Yi Wang wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> Could anyone give me a sense how many BGP routes a large ISP
>>>>>> typically
>>>>>> sees in total?
>>>>>> Here by "in total", I mean if the RIB of all routers in the
>>>>>> ISP were
>>>>>> merged, how many distinctive
>>>>>> routes would there be?
>>>>>
>>>>> Google(route bgp) "I am feelink lucky"
>>>>>
>>>>> aka first hit, and just look around there.
>>>>>
>>>>> Greets,
>>>>> Jeroen
>>>>>
