Quick question about inbound route-selection

Patrick W. Gilmore patrick at ianai.net
Sat Jul 18 06:02:55 UTC 2009

On Jul 16, 2009, at 7:05 PM, Wayne E. Bouchard wrote:
> On Thu, Jul 16, 2009 at 06:32:32PM -0400, Deepak Jain wrote:
>>> As for trying to determine where your inbound traffic is coming  
>>> from by
>>> looking at natural bgp, this is absolutely impossible to do  
>>> correctly.
>>> First off, your inbound is someone else's outbound, and the person
>>> sending the traffic outbound is in complete and total control. The  
>>> vast
>>> majority of the traffic on the Internet is being picked by local- 
>>> prefs
>>> based on policies like "what does this make/cost me monetarily" or
>>> "which major networks can I grab in a simple as-path regexp to  
>>> balance
>>> some traffic". But even if you ignore all of that, the "natural"  
>>> path
>>> selection is based on criteria which is specific to the other  
>>> network
>>> or
>>> even to a specific session which you can't possibly know about  
>>> remotely
>>> (e.g. their router id).
> I would actually disagree with that and go one step further. Look at
> content providers. They're not concerned about best path. They're not
> even concerned about shortest path. Since bandwidth consuming services
> are what they provide, they're interested in cheapest path as much as
> they are the shortest path.

s/content providers/some content providers, some eyeball networks,  
some corporate networks, and some of just about every type of network/

OTOH: Some content providers measure latency, packet loss, and  
throughput and react accordingly to ensure the end users get adequate  
performance, no matter the path or cost.

Interestingly, in either case, the 'natural' BGP selection is a poor  
predictor of inbound traffic.  But then we already knew that. :)


More information about the NANOG mailing list