[workfromspace]

About

> First, BGP generally prefers the shortest path and yours is going to be a little long, so unless the best original path is very long you need on some transit provider to use policy-based routing and trust you as transit.

the article states:

> The leaked route is likely preferable because of a localpref setting which would prefer sending traffic for free through a peer regardless of the AS path length, over paying to send traffic through a transit provider.

[Arnt]

Right. That's policy routing. You can talk to an ISP, have a cable installed and a peering session, gain trust, offer cheap or free traffic delivery, and then publish a route via that session. Your trusting peer may/will then send traffic to that route via you.

This happens legitimately, e.g. when an end-user becomes multihomed or starts using anycast, so the trusting peer can't necessarily discover this algorithmically. Route signing helps.