Refer to the exhibit. An engineer at a large ISP is troubleshooting suboptimal routing on a customer's IS-IS network with multiple Level 1-2 routers. The network consists of numerous routers that…

Question

Exhibit

Options

• ARedistribute Level 2 prefixes into Level 1 on router 2.
• BDisable advertisement of the default route on router 2.
• CConfigure each interface as either Level 1 or Level 2 circuit type on router 1.
• DConfigure the router as DIS for each of the interfaces on router 1.

• A
  73% (27)
• B
  16% (6)
• C
  3% (1)
• D
  8% (3)

Explanation

In IS-IS, Level 1 routers only maintain intra-area routing information. When they need to reach destinations outside their area, they rely on the closest Level 1-2 (L1/L2) router, which sets the 'attached bit' in its LSP to signal reachability to the Level 2 backbone. The problem is that Level 1 routers blindly route to the nearest L1/L2 router regardless of whether it leads to the optimal exit point - this is the root cause of suboptimal routing in Area 8 and Area 10. The fix is to redistribute Level 2 prefixes (inter-area and external routes) into the Level 1 domain on Router 2. This gives Level 1 routers full routing information about external destinations, allowing them to make topology-aware decisions rather than simply defaulting to the closest L1/L2 router. Option B is wrong (disabling the default route would break connectivity). Option C applies to interface circuit types, not the routing decision itself. Option D (DIS election) controls the designated IS on broadcast networks and is unrelated to suboptimal path selection.

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