Number of BGP routes a large ISP sees in total

Wed Apr 18 02:22:42 UTC 2007

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?

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?

-- 
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
>>>>