Which routing protocol uses cost as its primary metric to determine the best path?
Correct Answer: B
Detailed Explanation: Open Shortest Path First (OSPF) is a link-state routing protocol that uses cost as its primary metric for determining the best path through a network. In OSPF, cost is a value that is assigned to each interface based on its bandwidth, and it represents the expense associated with sending packets over that link. The protocol then uses these cost values to calculate the shortest, or least expensive, path from one router to another using Dijkstra’s Shortest Path First (SPF) algorithm. When OSPF is configured, each router collects information about its directly connected links, including the cost of each link. The cost is usually determined by a formula that takes the interface’s bandwidth into account, so that links with higher bandwidths have lower cost values. This design ensures that traffic is more likely to flow over faster, higher capacity links, leading to improved network performance. Once all routers in an area have exchanged their link-state information, each router builds a complete view of the network’s topology, called the link-state database. With this database, each router independently computes the best path to every other network destination using the SPF algorithm. The computed best paths are then installed into the routing table, and data packets are forwarded accordingly. Unlike RIP, which uses hop count as its metric, OSPF’s cost-based metric is more flexible and typically results in more optimal routing decisions. OSPF can differentiate between links with varying speeds and capacities, leading to a more efficient use of available network resources. This is particularly important in large, heterogeneous networks where the performance characteristics of links can differ widely. EIGRP, another dynamic routing protocol, uses a composite metric based on several factors such as bandwidth, delay, reliability, load, and MTU. While EIGRP’s metric is also designed to find optimal paths, it is not solely based on cost as defined in OSPF. BGP, on the other hand, uses a variety of attributes (such as AS path, local preference, and MED) rather than a simple cost metric to determine the best path for interdomain routing. OSPF’s reliance on cost as its primary metric is a fundamental aspect of its design. This approach ensures that the protocol is capable of adapting to a wide range of network conditions by favoring routes with lower costs. It also allows network administrators to manipulate routing decisions by adjusting interface costs, providing a degree of control over how traffic is distributed across the network. For network professionals, especially those preparing for the CCNA exam, understanding how OSPF calculates and uses cost is critical. This knowledge not only helps in designing efficient networks but also in troubleshooting routing issues. When a route is not being selected as expected, verifying the cost assignments on the relevant interfaces can often reveal misconfigurations or network anomalies. In summary, OSPF is the routing protocol that uses cost as its primary metric to determine the best path through the network. Its cost-based metric, combined with the SPF algorithm, allows OSPF to dynamically calculate optimal routes based on the available bandwidth and link quality, ensuring efficient and reliable data delivery in modern networks.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.