JN0-649: Enterprise Routing and Switching, Professional (JNCIP-ENT)

IS-IS leaks Level 1 routing information to Level 2 by default, but Level 2 routes are not advertised into a Level 1 area unless an explicit route-leaking policy is configured. With wide-metrics-only, extended reachability advertisements do not retain the internal-versus-external distinction needed to prevent Level 1 external routes from being leaked upward; the setting does not stop Level 1 routes from being advertised to Level 2.