Which parameter is NOT used in the default EIGRP composite metric calculation?
Correct Answer: C
Detailed Explanation: EIGRP (Enhanced Interior Gateway Routing Protocol) calculates a composite metric that determines the best path to a destination network. The composite metric is based on several parameters that reflect the quality and performance of a link. By default, EIGRP uses a formula that incorporates bandwidth and delay to calculate the metric. Parameters in the Calculation: Bandwidth: EIGRP considers the minimum bandwidth along the path. A higher bandwidth (i.e., a lower cost) results in a lower metric value, making that route more desirable. Delay: The total delay along the path is also summed up. Lower delays contribute to a lower overall metric, which indicates a better path. Reliability and Load: Although EIGRP has the capability to incorporate reliability and load into its composite metric, by default these parameters are not factored into the metric calculation. The default settings use only bandwidth and delay. Reliability and load can be manually configured if desired, but they are not part of the default metric. Why “Load” Is the Correct Answer: Since the default EIGRP metric calculation uses only bandwidth and delay, the parameter “Load” is not used unless an administrator specifically adjusts the settings. Therefore, Option C (“Load”) is the parameter that is NOT used in the default calculation. Importance in Network Design: Understanding how EIGRP calculates its metric is essential for network engineers. It helps in predicting which routes will be preferred and in troubleshooting routing decisions. For instance, if a link’s bandwidth decreases (perhaps due to congestion or hardware issues), the metric will increase, and EIGRP might select an alternative path if available. However, if load were a factor by default, temporary spikes in traffic might affect the routing decision. By default, excluding load from the calculation ensures stability and predictability in route selection. Comparison with Other Protocols: Different routing protocols use different metrics. For example, RIP relies solely on hop count, while OSPF uses a cost based on link bandwidth. EIGRP’s use of a composite metric that combines bandwidth and delay (with optional factors) provides a balance between simplicity and accuracy in representing link quality. Troubleshooting Implications: When diagnosing EIGRP routing issues, network engineers should focus on changes in link bandwidth and delay. Tools such as “show ip eigrp interfaces” can display the current metric components for each interface, confirming that load is not being factored by default. Conclusion: In the default EIGRP composite metric calculation, the parameters used are bandwidth and delay. The parameter “Load” is not used unless specifically configured. Therefore, Option C (“Load”) is the correct answer, as it is not part of the default metric calculation.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.