A large enterprise network running IS-IS wants to deploy IGP traffic engineering, but they are concerned that the IS-IS default metrics are not flexible enough. Which feature must be enabled to…

Question

Options

• AIS-IS Narrow Metrics
• BIS-IS DIS
• CIS-IS Wide Metrics
• DIS-IS Multitopology

• A
  10% (5)
• B
  6% (3)
• C
  81% (42)
• D
  4% (2)

Explanation

IS-IS Wide Metrics (option C) must be enabled because IS-IS default ("narrow") metrics use only a 6-bit link metric (values 0–63) and a 10-bit path metric (0–1023), which lack the granularity and range needed for MPLS Traffic Engineering; wide metrics expand these to 24-bit link and 32-bit path values and introduce the TE-specific TLVs (TLV 22, 135) that carry bandwidth and affinity information TE requires. Simply enabling wide metrics is the minimum change - no topology redesign or new protocol is needed. Option A (Narrow Metrics) is the existing default that creates the problem, not the solution. Option B (DIS) refers to the Designated Intermediate System election on broadcast segments, which is unrelated to metric scaling or TE. Option D (Multitopology) allows IS-IS to maintain independent topologies for different address families (e.g., IPv4 vs. IPv6), which is a much heavier change and not required for basic TE deployment.

Memory tip: Think "TE needs wide lanes for traffic to flow" - just as a wide road handles more traffic, IS-IS Wide Metrics provide the larger numerical range and extended TLVs that Traffic Engineering calculations depend on.

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