Which command is used on a Cisco device to display the current ARP table?
Correct Answer: B
Detailed Explanation: The Address Resolution Protocol (ARP) is responsible for mapping Layer 3 IP addresses to Layer 2 MAC addresses on a local network. This mapping is stored in an ARP cache (or ARP table) on a network device. On Cisco devices, the command used to display the ARP table is “show ip arp”. What “show ip arp” Displays: When you run “show ip arp” in privileged EXEC mode on a Cisco router or switch, the device displays the ARP table entries. These entries typically include the following information: IP Address: The Layer 3 address of the device. MAC Address: The corresponding Layer 2 hardware address. Type: The type of ARP entry (e.g., dynamic or static). Interface: The local interface through which the device is reachable. This information is vital for troubleshooting issues related to address resolution, connectivity, and Layer 2 network problems. Importance for Troubleshooting: Verifying the ARP table is a common troubleshooting step when devices are having difficulty communicating on a network. For instance, if a device is unable to reach a destination, checking the ARP table helps determine whether the correct MAC address is being resolved for the destination IP. An empty or incorrect ARP table may indicate problems such as connectivity issues, misconfigurations, or even security attacks like ARP spoofing. Comparison with Other Options: Option A (“show arp table”): Although the wording might seem logical, this is not a valid Cisco IOS command. Option C (“display arp”): This syntax is not used in Cisco IOS; it might be found in other operating systems. Option D (“show mac address-table”): This command displays the MAC address table for a switch, which shows the mapping between MAC addresses and switch ports. It does not show the ARP mappings between IP addresses and MAC addresses. Usage Example: To view the ARP table, enter: Router# show ip arp This command will list all the dynamic and static ARP entries. Network administrators can then verify that the correct MAC addresses are associated with known IP addresses. Conclusion: The “show ip arp” command (Option B) is the correct command to display the current ARP table on a Cisco device. Understanding and using this command is essential for troubleshooting and verifying that devices on the network are correctly resolving IP addresses to their corresponding MAC addresses.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.