Refer to the exhibit. An engineer is addressing an IS-IS design issue which is running within the topology. All links are running on FastEthernet, except the link between R5 and R4, which is Gigabit…

Question

Exhibit

Options

• AR4 prefer to reach R5 using R1 as the next hop
• BAll links have equal cost if the default metric is used
• CR5 prefers to use R4 as the next hop for all routes
• DR1 prefer to use R5 as the next hop to reach R4

• A
  9% (2)
• B
  87% (20)
• C
  4% (1)

Explanation

IS-IS, unlike OSPF, does not automatically derive interface cost from bandwidth. By default (using the narrow/default metric), IS-IS assigns a metric of 10 to all interfaces regardless of their speed or type. This means a FastEthernet link and a GigabitEthernet link both have an IS-IS cost of 10 by default. As a result, all links in the topology have equal cost, and no link is preferred over another based on bandwidth alone - unless the administrator manually configures different metrics or enables the wide metric with interface-speed-based costing. Options A, C, and D describe preferences that would only exist if costs were unequal, which is not the case with default IS-IS metrics.

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