Which of the following do you need to take into account when designing multitopology IS-IS? (Select two.)

Question

Options

• AMultitopology IS-IS should be avoided when IPv4 coexists with IPv6 in the same network.
• BWhen multitopology for IPv6 is used, IS-IS wide metric should be considered.
• CIn migration scenarios (moving from single to multitopology), you should consider the
• DAll routers must be configured as L1.
• EAll routers must be configured as L2.
• FSingle SPF process will be carried for all the configured topologies.

• A
  10% (3)
• B
  65% (20)
• D
  16% (5)
• E
  3% (1)
• F
  6% (2)

Explanation

B is correct: Multitopology IS-IS maintains separate SPF trees for different address families (e.g., IPv4 and IPv6). When IPv6 topology is enabled separately, IS-IS wide metrics (32-bit, using TLV 22/135) should be used because they support the extended TLVs required for multitopology operation and provide more granular metric values needed for accurate path selection and MPLS-TE extensions. C is correct: Migrating from single topology to multitopology IS-IS is not seamless. During the transition, some routers will be in single topology mode while others are in multitopology mode, which can cause routing inconsistencies and potential black holes. Careful staged migration and understanding of the transition mechanism (IS-IS MT transition TLVs) is required. A is false because multitopology IS-IS is actually the recommended solution when IPv4 and IPv6 need different paths - it allows each family to have its own independent SPF. D and E are false because multitopology IS-IS does not require all routers to be a specific level. F is false because multitopology IS-IS runs SEPARATE SPF processes for each topology, which is the entire point of the feature.

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