300-320 Question #652: Real Exam Question with Answer & Explanation

The correct answer is A: Hub-and-spoke interfaces must be configured with the same network type.. IS-IS over NBMA hub-and-spoke requires careful interface configuration for adjacencies to form correctly. (A) IS-IS requires that neighboring interfaces share the same network type - if one side is configured as point-to-point and the other as broadcast, the adjacency will not es

Question

Which of the following do you need to take into account when designing IS-IS over NBMA hub- and-spoke topology? (Select two.)

Options

AHub-and-spoke interfaces must be configured with the same network type.
BHub interfaces can be configured as multipoint, while spokes should be configured as point- to-
COnly L2 must be used over the NBMA network.
DHubs must be configured as L1/L2, whereas the spokes must be configured as L1 only.
EHub WAN interfaces should be configured with point-to-point subinterfaces, whereas the spokes

Explanation

IS-IS over NBMA hub-and-spoke requires careful interface configuration for adjacencies to form correctly. (A) IS-IS requires that neighboring interfaces share the same network type - if one side is configured as point-to-point and the other as broadcast, the adjacency will not establish. Consistency is mandatory. (E) The recommended design is to configure hub WAN interfaces as point-to-point subinterfaces - one subinterface per spoke - with each subinterface treating the hub-to-spoke circuit as a dedicated point-to-point link. Spoke interfaces are similarly configured as point-to-point. This eliminates NBMA multipoint neighbor discovery complexity, avoids DIS election issues, and provides a clean, scalable topology. Option B describes a mixed multipoint/point-to-point configuration that would violate the matching requirement in A. Option D describes a mixed L1/L2 configuration that is not specific to NBMA design.

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