On a Cisco router, which command displays the current ARP table showing IP-to-MAC address mappings learned on the interfaces?

Introduction / Context:
This question tests your familiarity with Cisco IOS commands for viewing ARP information. On routers, ARP plays a crucial role in mapping next hop IP addresses to local MAC addresses so that packets can be forwarded correctly onto Ethernet and other broadcast media. Knowing how to display the ARP table is essential for troubleshooting local connectivity issues.

Given Data / Assumptions:
- We are using a Cisco router running IOS or a similar operating environment.
- We want to see the ARP table, which maps IP addresses to hardware (MAC) addresses for connected networks.
- The question asks for the specific show command that displays this information.

Concept / Approach:
The show ip arp command on Cisco routers displays the ARP table for IPv4. It shows protocol type, the IP address, age, hardware address, and interface. This table is populated as the router communicates with devices on directly connected networks. Other commands such as traceroute and show mac-address-table have different purposes related to path tracing or switch CAM tables.

Step-by-Step Solution:
Step 1: Recall that ARP is used on routers to resolve next hop IPv4 addresses into MAC addresses on local segments.Step 2: On Cisco IOS, remember that many diagnostic commands are accessed with the show keyword.Step 3: Recognize that show ip arp is the standard command to list ARP entries for IPv4 on routers.Step 4: Note that commands like arp -a are used on Windows, not on Cisco IOS.Step 5: Select show ip arp as the correct answer.

Verification / Alternative check:
In a lab or production environment, you can execute show ip arp on a Cisco router and observe the output. Entries typically include the IP address of directly connected hosts and routers, their MAC addresses, and the interface on which they were learned. Clearing the ARP cache and then generating traffic will cause new entries to appear, confirming that the command is tied directly to ARP resolution.

Why Other Options Are Wrong:
The traceroute and tracert commands display hop by hop paths but not ARP mappings. The arp -a command is specific to Windows hosts, not Cisco routers. show mac-address-table is used primarily on switches to display which MAC addresses have been learned on which ports and VLANs; it is related but distinct from the ARP cache maintained on routers.

Common Pitfalls:
One pitfall is to confuse the switch MAC address table with the router ARP table, since both involve MAC addresses. Another is to assume that the same arp -a syntax applies across platforms. Remember that on Cisco routers, show ip arp is the correct way to inspect ARP entries for IPv4, whereas other commands focus on different aspects of network operation.

Final Answer:
The Cisco router command show ip arp displays the ARP table with IP-to-MAC address mappings.