4A0-112: Nokia IS-IS Routing ProtocolDemo

By Nokia · Question Mode

QuestionQ18

SR OS Control Plane Security

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In the IS-IS network shown, R1 is configured to summarize the 20.20.1.0/24 and 20.20.2.0/24 subnetworks as 20.20.0.0/16. Compared with their routing tables before summarization, which routers will have reduced routing tables?

  • A Router R1
  • B Router R2
  • C Routers R1 and R2
  • D Routers R2 and R4
Explanation

An IS-IS Level 1/Level 2 router can summarize Level 1 prefixes when advertising them into Level 2, replacing multiple specific prefixes with one aggregate for Level 2 routers. R1 still needs the two specific Level 1 routes within Area 49.0001, while R2 learns the single 20.20.0.0/16 aggregate instead of both /24 routes. A Level 1-only router in the other area does not receive those interarea specifics; it uses its Level 1/Level 2 router for external-area reachability.

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