Anycast networks serve clients from whichever Point of Presence is closest — in theory. In practice, BGP routing makes opaque decisions that often send traffic to distant PoPs. The operator can see the misrouting but has limited tools to fix it.
AS-path prepending — artificially lengthening the advertised path to a PoP to make it less attractive — is one of the few available levers. But using it effectively requires knowing which clients are sensitive to prepending and how they'll reroute. Without that knowledge, prepending is trial and error.
The authors (arXiv:2603.21082) build AnyPro, which systematically identifies all prepending-sensitive clients via efficient polling, extracts routing constraints from observed changes, and solves for the globally optimal prepending configuration. On a 20-PoP testbed, AnyPro reduces 90th-percentile latency by 37.7%.
The through-claim: the steering mechanism already exists in BGP — prepending changes routing decisions. What was missing was the map: which clients respond to which prepends, and what configuration minimizes latency globally. AnyPro doesn't change the protocol; it solves the optimization problem that the protocol's complexity made intractable by trial and error.