Which statements are true about IS-IS routing? (Select two.)

Question

Options

• ABy default, L1-only routers will receive only a default route from the L1/L2 border routers.
• BBy default, L1-only routers can receive only default route + summary from the L1/L2 border
• CL1-only routers can receive a default route + more specific from the L1/L2 border routers, if route
• DL1-only routers can receive a default route only from the L1/L2 border routers, regardless whether
• EThe default route will not be injected into an L1 area from the L1/L2 border routers by default.

• A
  77% (20)
• B
  4% (1)
• D
  8% (2)
• E
  12% (3)

Explanation

A is correct: By default, when an L1/L2 border router detects that it has connectivity to the L2 backbone, it sets the 'attached' bit in its L1 LSPs. This signals to L1-only routers that a default route should be used to reach destinations outside the L1 area. L1-only routers install a default route pointing toward the nearest L1/L2 border router - they do not receive the full L2 routing table. C is correct: IS-IS supports route leaking, a feature that allows L1/L2 border routers to selectively inject specific L2 prefixes (more specific routes) into the L1 LSDB. When configured, L1-only routers receive both a default route and these leaked, more-specific L2 prefixes, enabling more precise routing decisions. B is false because summaries are not leaked by default - only a default route is. D is false because route leaking CAN cause L1-only routers to receive more than just a default route. E is false because the default route IS injected into L1 areas by default via the attached bit mechanism.

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