When set to true, allows this router to leak (redistribute) routes learned at Level 2 (the backbone) down into its Level 1 (intra-area) LSPs, giving L1-only routers in the area more specific routing information than just the default attached-bit route toward L2. An admin enables this on an L1L2 border router when area routers need better-than-default routes to specific external destinations rather than relying solely on the nearest-L1L2-router default.