Which of the following statements are true about IS-IS route leaking? (Select two.) A. It is done at L1璍2 routers.

Question

Options

• BFor a prefix to be leaked, it must exist in the routing table as IS-IS Level 1 route.
• CYou can use route leaking to solve suboptimal routing.
• DAn up/down bit in the CDP field is used.
• EYou need to disable all loop protection mechanisms.

• B
  4% (1)
• C
  69% (18)
• D
  8% (2)
• E
  19% (5)

Explanation

IS-IS route leaking is the process of redistributing Level 2 (backbone) routing information down into Level 1 (area) routing tables. Without route leaking, L1-only routers send all traffic to the nearest L1/L2 router for exit, which may not be the optimal path - route leaking solves this suboptimal routing problem by giving L1 routers visibility into specific L2 destinations (C is correct). The up/down bit is set in the IP reachability TLV field (not the CDP field as stated in D) to mark leaked routes and prevent them from being re-leaked back upward, which would cause loops. Option B is incorrect - route leaking moves L2 routes downward into L1 areas, not L1 routes upward. Option E is incorrect - the loop prevention mechanism (the up/down bit) must remain active and must not be disabled.

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