Symptom
VPLS/EVPN BUM traffic is black holed on imposition PE when the traffic is forward on interAS BGP routes.
Conditions
The BGP routes are over bundle interfaces and the backup routes are also on bundle interface. The problem is triggered by bundle member state change on primary BGP paths. If the bundle on backup path has bundle member state change within 100ms of bundle member state change on primary paths, there is chance that BUM traffic is forwarded over bundle members which went down. This caused traffic black hole.
Workaround
The workaround is not to put BGP backup paths over multi-member bundle interfaces.
Further Problem Description
The problem is not easily hit in production network. The chance of bundle member state changes on both primary and backup BGP paths within 100ms interval is very slim. If the problem is hit, the recovery step is to flap a bundle member on primary BGP path.
