Inferring the location points of traffic exchange between two networks

Wed Jan 13 17:46:27 UTC 2016

The fastest way to get this information first-hand would be to set up a
network in an emulator (GNS3, VIRL, PacketTracer, etc). There are hundreds
of guides online to do this. Then you could do the same show commands and
record the output.

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-----Original Message-----
From: NANOG [mailto:nanog-bounces at nanog.org] On Behalf Of Reza Motamedi
Sent: Wednesday, January 13, 2016 12:36 PM
To: nanog at nanog.org
Subject: Inferring the location points of traffic exchange between two
networks

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