Cisco Certified Network Associate (CCNA) Practice Exam

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What command enables CDP on a router?

(config)# cdp enable
(config)# cdp start
(config)# cdp run
(config)# enable cdp

The correct answer is: (config)# cdp run

The command that enables Cisco Discovery Protocol (CDP) on a router is indeed "cdp run". This command activates CDP globally, allowing the router to start sending and receiving CDP packets on its interfaces. CDP is a Layer 2 protocol that helps network devices discover information about other directly connected Cisco devices, such as their platform, capabilities, and IP addresses, thus aiding in network management and topology comprehension. The other commands listed do not provide the correct syntax for enabling CDP globally. The command "cdp enable" does not exist in this context in Cisco IOS, and neither do "cdp start" or "enable cdp". Therefore, "cdp run" is the accurate and recognized command within Cisco's IOS for activating this protocol on the device.