Using ARP to Locate a Duplicate IPv4 Address Node
Short answer
B Use arp -a to read the IP-to-MAC mapping for the duplicate IPv4 address, then trace that unique MAC to the switch port and offending node.
Question
Key Takeaways
This question tests the boundary between reachability testing and Layer 2 identity resolution; the trap is selecting ping, which can reveal a live conflict but cannot identify the MAC or physical node.
A duplicate IP address requires resolving the disputed IPv4 address to a unique MAC address, not just proving reachability. On this N10-009 question, arp (B) is the command that exposes that IP-to-MAC mapping so the node can be traced.
Common mistake: The most plausible wrong answer is ping (A): it may confirm that the duplicate address responds, but it does not expose the MAC address needed to locate the offending node—arp does.
Expert Analysis
The boundary: identity versus reachability
The common confusion here is treating ping and arp as interchangeable diagnostics. ping sends ICMP Echo requests to test whether an IP address is reachable; it answers “can I communicate with this address?” arp displays the ARP cache, the IP-to-MAC binding table that maps a Layer 3 address to a Layer 2 hardware address. A duplicate-IP warning requires the second question: “which physical NIC is using this address?” That is an identity question, not a connectivity question, so it lands on arp.
Why the scenario falls on the ARP side
An IP address may be duplicated, but a NIC’s MAC address normally is unique. arp -a (or ip neigh on Linux) reveals the MAC associated with the disputed IPv4 address. After clearing the cache and pinging the address to repopulate it, the administrator can take that MAC, look it up in the switch’s MAC address table, and trace the port or device. The reasoning in the discussion correctly focuses on this IP-to-MAC mapping: the unique MAC is what enables tracking down the port or physical device.
Why the other options miss
ping (A) may confirm that the duplicated address responds, but it does not return the identity of the responder, so it cannot by itself locate the node. ipconfig (C) shows the local host’s addressing and may report a duplicate-address conflict on that host, but it does not enumerate remote mappings. nslookup (D) queries DNS for name-to-address resolution, which is unrelated to an on-link duplicate IPv4 address. The correct command is therefore B. arp.
Official Reference
- https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/arp
- https://www.rfc-editor.org/rfc/rfc826
- https://www.comptia.org/certifications/network
These links open the official vendor documentation in a new tab.
Exam Strategy
When a question asks you to locate, identify, or trace a host by IP, scan the options for the command that exposes Layer 2 identity. ping tests reachability, ipconfig displays local configuration, nslookup resolves DNS names, and arp shows IP-to-MAC mappings. Map the stem’s verb to the right tool: choose ARP for identity and the switch MAC table for the physical port.
Frequently Asked Questions
Why does arp -a help locate a duplicate IP address?
Can ping identify which device owns a duplicate IP?
What should I do after finding the MAC with arp?
Community Votes
100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 1 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 1
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ERB14 👍 1 Answered Barp (Address Resolution Protocol): The arp command (e.g., arp -a) displays the IP-to-MAC address mapping table on a device. Since every network interface card (NIC) has a unique MAC address, viewing the ARP table allows the administrator to find the MAC address associated with the duplicate IP address. Once the MAC address is identified, the administrator can track down the physical port or device on the switch
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