On Tue, Mar 8, 2022 at 2:36 PM Sriram, Kotikalapudi (Fed) <kotikalapudi.sriram=40nist....@dmarc.ietf.org> wrote:
> This question has relevance to the ASPA method for route leak detection. > > Is it possible that an ISP AS A peers with a customer AS C via a > non-transparent IXP AS B? > IOW, the AS path in routes propagated by the ISP A for customer C's > prefixes looks like this: A B C. > I.e., can the AS of a non-transparent IXP/RS appear in an AS path in the > middle between an ISP and its customer? > > it seems unlikely to me that an ISP would pick up a 'customer' (someone that pays them to transport packets) at an IXP fabric. Might it happen? sure? is it messy? yes! 1) that's probably a shared port 2) there are other folk feeding routes and packets into the mix 3) how many came through the 'customer' port (which you can't really know easily) vs other participants on the ix 4) what capacity planning could the 'customer' do here? (none, basically with respect to the remote ISP port) Your question might work also as: "ISP A has a customer C on a direct link in location Y. ISP A is present at IXP-Z, so is customer C, though they do not bilaterally peer (not do they interconnect at the IXP). ISP A can still see Customer C's routes through the IXP-Z Route Server." that seems plausible, but not a desired outcome for the ISP :) since they will be unlikely to collect pesos for the traffic which MAY pass across that interconnect.
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