Which Cisco IOS command is used to display the current routing table on a router?
Correct Answer: B
Detailed Explanation: The command "show ip route" is used in Cisco IOS to display the current routing table on a router. The routing table is a critical data structure within a router that lists the routes to various network destinations. Each route in the table includes the destination network, the next-hop address, the outgoing interface, and metric information, which the router uses to determine the best path for forwarding packets. When you enter the "show ip route" command on a Cisco router, the device prints a detailed list of all known routes. These routes can be learned through different means, such as directly connected networks, static routing configurations, and dynamic routing protocols like OSPF, EIGRP, or RIP. The output of this command provides valuable insights into the network’s topology and helps network administrators troubleshoot connectivity issues and verify that routing protocols are functioning as expected. Dynamic routing protocols populate the routing table by exchanging routing information with neighboring routers. For example, when using OSPF, routers share link-state information to build a complete view of the network topology. The "show ip route" command will then list OSPF routes along with their administrative distances and metric values. For static routes, which are manually configured, the command will display the specific network destinations along with the fixed next-hop addresses defined by the administrator. Another benefit of the "show ip route" command is that it displays the source of each route. In Cisco IOS output, different letters or symbols indicate how a route was learned. For instance, routes marked with a “C” denote directly connected networks, while those marked with an “S” are static routes. Routes learned via OSPF are often marked with “O” and EIGRP routes with “D.” This labeling helps administrators quickly understand the origin and reliability of the routes. Understanding the routing table is essential for maintaining network performance and security. If a router’s routing table is not properly populated or contains incorrect routes, data packets may be misrouted or dropped entirely, leading to network outages or degraded performance. Regularly reviewing the routing table with "show ip route" helps ensure that all intended routes are present and that the network is resilient to changes or failures. Moreover, the command output may include summary information such as default routes (usually marked as “S*”) and various subnets. This comprehensive view aids in verifying that all network segments are reachable and that the routing policies are correctly enforced. Advanced users can combine this command with filtering techniques or additional options to focus on specific types of routes, further enhancing troubleshooting efficiency. For a network professional preparing for the CCNA exam, mastering the use of the "show ip route" command is crucial. It not only confirms the functionality of routing protocols but also provides a foundation for more advanced tasks like route redistribution and policy-based routing. Regular practice with this command in lab environments builds the confidence and skills necessary to manage complex 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.