GRES and L2TP Failover: LAC support

Graceful Routing Engine switchover (GRES) is supported on routers acting as the L2TP access concentrator (LAC) when L2TP (the L2TP Universal Edge process) restarts or the router fails over from the active Routing Engine to the standby Routing Engine. The LAC supports both the L2TP failover protocol method and the L2TP silent failover method for peer resynchronization with a failed remote endpoint.