Which of the following descriptions of routing protocol cost values (Cost) is incorrect?

Question

Options

• ABy adjusting the cost value of the route, the suboptimal path problem in certain scenarios can be solved.
• BThe routing cost calculation methods of different routing protocols are generally different, so the Cost values of different routing protocols are not comparable.
• CWhen different routing protocols introduce each other, the Cost value must be manually specified, otherwise the introduction cannot be normal.
• DUsually the Cost unit of IS-IS and OSPF is based on bandwidth and has a wide value range, which can be applied to larger-scale networks.

• A
  7% (2)
• B
  4% (1)
• C
  74% (20)
• D
  15% (4)

Explanation

Option C is incorrect because when routing protocols redistribute routes from one another, routers apply default seed metrics automatically if no cost is manually configured, so normal redistribution can still occur without manual intervention. The claim that manual specification is required for redistribution to work is too absolute and does not reflect actual router behavior, where built-in defaults handle the metric assignment.

Option A is correct: administrators routinely manipulate cost values to steer traffic away from suboptimal paths, which is a standard traffic-engineering technique. Option B is correct: OSPF derives cost from bandwidth, RIP uses hop count, and BGP uses path attributes, so their cost values are fundamentally incompatible and cannot be directly compared. Option D is also correct: both OSPF and IS-IS support wide metric ranges suited for large networks, and OSPF cost is bandwidth-based while IS-IS wide metrics can also reflect bandwidth.

Memory tip: Think of C as the "must" trap. Exam questions that use absolute words like "must" or "cannot" are often the incorrect choice in networking, because routing protocols are designed with sensible defaults so that redistribution works even without administrator intervention.

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