Let's say you do not want the traffic destined to your /8 prefix to traverse AS Y. How would you modify your BGP configuration to do that?

Thank you for your time

1 Answer 1


How would you modify your BGP configuration to do that?

You don't. An AS is an Autonomous System. You have control of your AS, but you do not control any other AS, just as you do not want someone else to have control of your AS. How other ASes route your traffic is basically none of your business.

You can give hints to a neighboring AS with MED for which interface traffic to your AS should take, but that only works if the AS administrator agrees, and only if you have multiple connections to that AS. You can also advertise prefixes with prepended ASes, but other ASes are free to ignore that too. You can also enter into business agreements with your neighboring ASes, but those agreements do not affect other ASes in the public Internet.

You don't want anyone else telling you how to route traffic in your AS, and neither do the administrators of other ASes.

  • In a nutshell, (a) don't announce it to AS Y (assuming you're connected to them), and (b) set the appropriate community(s) to tell your upstream to not announce it to AS Y (assuming your peer(s) support doing so)
    – Ricky
    May 1, 2018 at 2:44
  • 2
    @RickyBeam, if AS Y is several ASes removed from you or your peer AS(es), you cannot be sure that it will not end up with a route to your prefix.
    – Ron Maupin
    May 1, 2018 at 2:50

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