Cisco Certified Network Associate (CCNA) Practice Exam

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What is the formula used by OSPF to calculate cost?

cost = actual bandwidth / 100000000
cost = 100000000 / actual bandwidth
cost = actual bandwidth * 100000000
cost = 100 / actual bandwidth

The correct answer is: cost = 100000000 / actual bandwidth

The correct formula used by OSPF (Open Shortest Path First) to calculate cost is based on the relationship between bandwidth and cost. The formula is cost = 100,000,000 / actual bandwidth. OSPF assigns a cost to each interface, which is inversely proportional to its bandwidth. The purpose of this calculation is to allow OSPF to make routing decisions based on the most efficient paths through the network. By using the higher value of 100,000,000, which represents the reference bandwidth in Kbps, OSPF allows for a standardized comparison across different interfaces that may have varying speeds. When an interface has a higher bandwidth, the resulting cost will be lower, which makes it more preferred for routing. Conversely, if the interface has a lower bandwidth, its cost will be higher, making it less preferred. This method encourages the routing of data across faster links, optimizing overall network performance. Overall, the chosen formula effectively reflects the OSPF routing metric and helps in making intelligent routing decisions based on the available bandwidth on the links.