I’m a huge fan of flapping when it’s really hard to do progressive rollouts. What this would mean here is you switch advertising the old and new routes back and forth automatically and this happens let’s say for 1 minute max before the old config is restored. Then a human looks at various metrics before they push a button to really make the new config permanent. It gives you a cheap way to preflight what will happen when you make a globally impacting config change.

I’m not sure this would be a good idea in this kind of change.

Flapping is bad in the networking world.

Flapping BGP routes, specifically, is bad because it can stress all BGP routers involved to the point where they can “go crazy”. Routes are explicitly advertised, so if you keep changing the routes, you are tasking the router CPU to process new stuff, discard it and process new stuff. In fact, BGP route flaps are specifically the focus of an entire RFC: https://datatracker.ietf.org/doc/html/rfc2439

More in general, a flapping link (on/off/on/off) can really mess with TCP.

Flapping in the networking world is not something you want to do intentionally.

nice way to 100% the router CPUs for all your peers