Which statement correctly describes the metric used for IS-IS?
Click on the arrows to vote for the correct answer
A. B. C. D.B
The protocol IS-IS does have an ability to use reference bandwidth to dynamically calculate link costs, but the default behavior has a value of 10 assigned to all transit interfaces.
IS-IS (Intermediate System to Intermediate System) is a link-state routing protocol that is widely used in large service provider and data center networks. IS-IS uses a metric to determine the cost of a path through the network, and the shortest path with the lowest metric is chosen as the best path to reach a destination.
Now let's take a look at each answer choice to see which statement correctly describes the metric used for IS-IS:
A. The IS-IS metric is calculated based on a reference bandwidth of 10 Mbps by default. This statement is correct. The IS-IS metric is calculated based on a reference bandwidth of 10 Mbps by default. The metric is proportional to the link speed, with slower links having higher metric values.
B. By default, IS-IS interface routes are assigned a metric of 10, regardless of actual link speed. This statement is incorrect. By default, IS-IS interface routes are assigned a metric based on the link speed, which is calculated using the reference bandwidth of 10 Mbps. Slower links will have a higher metric value.
C. By default, the Junos OS sends only wide metrics to allow any single link to have a metric as high as 63. This statement is partially correct. By default, the Junos OS sends only narrow metrics, which allow any single link to have a metric as high as 63. Wide metrics, which can be used to represent larger metric values, are optional and are not sent by default.
D. For proper operation, the same metric value should be specified at both ends of an IS-IS link. This statement is also correct. For proper operation, the same metric value should be specified at both ends of an IS-IS link. If the metric values are different at each end of the link, the routing information may be inconsistent, which can cause suboptimal routing or even network outages.
In summary, the correct statement that describes the metric used for IS-IS is A - The IS-IS metric is calculated based on a reference bandwidth of 10 Mbps by default, and statement D is also correct for the proper operation of IS-IS links.