The answer is the `arp -a` command, because it displays the local ARP cache, which maps IP addresses to their corresponding MAC addresses. When you need to check for an IP conflict, running `arp -a` after a broadcast ping reveals whether another device’s MAC address is already cached for that IP, indicating the address is in use even if the ping got no reply. On the CompTIA A+ Core 1 220-1201 exam, this question tests your ability to troubleshoot static IP assignment failures—a common trap is assuming “no ping reply” means the IP is free, when in fact a silent device or a cached entry from a prior response can cause a conflict. The key insight is that `arp` works at Layer 2, so it catches conflicts that ICMP might miss. Memory tip: think “ARP-a for ARP cache, IP-MAC match to avoid a clash.”
220-1101 Networking Tools Practice Question
This 220-1201 practice question tests your understanding of networking tools. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A technician is configuring a small office network and needs to assign a static IP address to a printer. The technician pings the intended IP address and gets no reply, but the printer still fails to communicate after configuration. Which tool should be used to verify that no other device on the network is using that IP address?
Why wrong: Continuous ping may show responses if the IP is in use, but it doesn't reveal the MAC address of the responding device.
B
arp -a
arp -a displays the ARP table, which lists IP addresses and their associated MAC addresses, helping confirm if the IP is already assigned to another device.
C
ipconfig /all
Why wrong: ipconfig /all shows the local computer's IP configuration, not the IP usage of other devices on the network.
D
Netstat -r
Why wrong: Netstat -r displays the routing table, which is not directly useful for checking IP address conflicts.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
arp -a
The arp command shows the IP-to-MAC address mappings in the local ARP cache. If another device responded to a ping earlier, its MAC might be cached, or the technician can use arp -a to check for existing entries. However, a more reliable method is to use a network scanner or check the DHCP server logs. In this context, arp helps verify if the IP is already in use by checking the cache after a broadcast.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Ping -t
Why it's wrong here
Continuous ping may show responses if the IP is in use, but it doesn't reveal the MAC address of the responding device.
✓
arp -a
Why this is correct
arp -a displays the ARP table, which lists IP addresses and their associated MAC addresses, helping confirm if the IP is already assigned to another device.
ipconfig /all shows the local computer's IP configuration, not the IP usage of other devices on the network.
✗
Netstat -r
Why it's wrong here
Netstat -r displays the routing table, which is not directly useful for checking IP address conflicts.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Trap categories for this question
Command / output trap
Continuous ping may show responses if the IP is in use, but it doesn't reveal the MAC address of the responding device.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 220-1201 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 220-1201 subnetting questions on CIDR, address ranges, and subnet selection.
Networking Tools — This question tests Networking Tools — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: arp -a — The arp command shows the IP-to-MAC address mappings in the local ARP cache. If another device responded to a ping earlier, its MAC might be cached, or the technician can use arp -a to check for existing entries. However, a more reliable method is to use a network scanner or check the DHCP server logs. In this context, arp helps verify if the IP is already in use by checking the cache after a broadcast.
What should I do if I get this 220-1201 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 220-1201 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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