Quick question about inbound route-selection

Deepak Jain deepak at ai.net
Thu Jul 16 22:32:32 UTC 2009

> 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).

Another way to say what Richard is getting at (which was full of good information) is:

Just because you aren't modifying what your BGP process sees, at this stage of the Internet's maturity, it is safe to assume almost everyone else is. Therefore, rather than pray for BGP to make a logical selection, even though its *probably* being fed prefs based on other people's engineering, you should take charge of the parts you can.


Deepak Jain

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