It’s common to think that a network has no way to break a leak if it has happened. You can’t configure proper filters at the router that is out of your control. Of course, you can start writing emails to responsible parties, and this may speed up the remediation process, but it will not instantly return your traffic.

But there is another way to restore proper connectivity, we can exploit the BGP loop detection mechanism: a network MUST automatically drop route if AS Path includes its own AS number. So, if you know the source of the problem, you can add “leaker” AS in your prepend policy, thus forcing it to reject this route.

Such AS Path manipulation complements monitoring service and provides a guaranteed method to actively fight route leak incidents. But you should be careful to keep 'valid' result of ROA validation procedure.

Ingénieux. :)

Via https://twitter.com/bortzmeyer/status/1067339854416134144.