A single hijacked prefix can route a chunk of payment traffic into a stranger's network for half an hour before anyone notices. For a payment provider, that is not a routing incident. It is a regulatory event, an exposed-traffic incident, and an auditor knocking on Monday morning.

This post walks through the BGP edge hygiene we ran in production at a national fintech: what we filtered, how we automated it, what broke, and a copy-paste checklist at the end.

The threat model in 200 words

If you run a public-facing AS, the internet routing system trusts you and your peers to announce only what you should announce. That trust is not enforced by default.…