BGP zombies are routes in the BGP table that refuse to disappear even though they should have been long gone. Recent measurements estimate between 0.5% and 1.5% of all routes in the global BGP table are zombies, which sounds crazy – after all, BGP is supposed to be pretty reliable.

Daryll Swer identified one potential source – Juniper routers do not revoke suppressed aggregated prefixes – and documented it in Navigating a BGP zombie outbreak on Juniper routers.