Inferring the location points of traffic exchange between two networks

Wed Jan 13 17:36:03 UTC 2016

Hi NANOG,

I am researcher at the University of Oregon and my question is rather
primitive. My research background is in networked systems and Internet
measurement so I know how things work in theory.

My question is about BGP and what can be inferred from the output of
different "show" commands, regarding the point of traffic exchange of two
networks with different ASNs. I tried going through the some samples on
Juniper and Cisco documentations but I did not get my answer.

Consider the following scenario; Say the point of traffic exchange between
AS_a and AS_b is in San Francisco and we run "show bgp summary" and "show
ip bgp <prefix>"on a BGP router of AS_a in LA. Do we see the peering
between AS_a and AS_b in San Francisco using any of the two commands. If
yes is there a way to infer that in fact the traffic is not exchanged
locally in LA? I think there should be a flag to differentiate records
showing iBGP vs eBGP.

On the same note, if we issue the commands on a router other than the
border router in San Fran, is there any difference in the output of show
commands?

Now how are things different if we actually run the commands on that
gateway router in SF?

Best Regards
Reza Motamedi (R.M)
Graduate Research Fellow
Oregon Network Research Group
Computer and Information Science
University of Oregon