BGP zombies and excessive path hunting

Cloudflare analyzes BGP “zombie” routes—stale, withdrawn prefixes that persist due to path hunting, MRAI delays, and uneven convergence—showing how they cause routing loops and reachability problems, especially when withdrawing more-specific announcements (e.g., during BYOIP on-demand operations). Using controlled experiments across IPv4/IPv6, the report quantifies zombie lifetimes from seconds to 10+ minutes, notes greater impact in IPv4, and recommends mitigations including staged cutovers with same-length prefixes, internal traffic draining akin to no-export behavior, and vendor adoption of RFC9687 to reduce stuck routes.