distinguishing eBGP from show ip BGP

Mark Tinka mark.tinka at seacom.mu
Wed Mar 11 20:36:35 UTC 2015


On 11/Mar/15 22:27, Reza Motamedi wrote:
> Thanks again, Mark.
>
> So I guess the short answer is that I can't infer anything about the 
> location of physical connectivity having this level of information 
> from the control plane.

Not reliably as far as I can tell, no. Someone else can chime in here if 
they have another perspective.

One could rely on traceroutes, but that is crude and sometimes 
unavailable if you're looking to gather any meaningful data (even though 
it might be the closest piece of information you'll get without engaging 
with the network operator).

> What if the "Next Hop" is inside the neighbor AS. I know it is a 
> rather odd and uncommon case, but can it help?

Control-plane-wise, that could be eBGP Multi-Hop.

Forwarding-plane-wise, that is likely a tunnel operation.

Technically, one can build such a topology. I'd hazard that at least 
someone is doing this out there somewhere. However, it's not typical by 
any means.

Mark.


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