DHCP Scope Exhaustion and APIPA: Troubleshooting Guide
A network administrator configures a small office with a router providing DHCP. A user's computer gets an IP address of 169.254.1.5. The user cannot access the internet. The technician checks the network cable and sees link lights. Which of the following is the MOST likely cause?
⚠ Common exam trap
The trap here is that candidates see link lights and assume Layer 1 is fine, then incorrectly blame DNS or subnet mask, missing that APIPA is the definitive symptom of a failed DHCP transaction.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The DHCP server is unreachable.
The IP address 169.254.1.5 is an Automatic Private IP Addressing (APIPA) address, which Windows assigns when a DHCP discovery broadcast fails to receive a response. Since the router is configured to provide DHCP but the client ended up with an APIPA address, the DHCP server is unreachable — likely due to a misconfigured DHCP relay, a disabled DHCP service on the router, or a VLAN mismatch blocking the broadcast. The link lights confirm Layer 1 connectivity, so the issue is at Layer 3 or above.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Incorrect subnet mask.
Why it's wrong here
An incorrect subnet mask would not trigger APIPA because the host would still successfully lease an address from DHCP if the server were reachable. The client would receive a valid IP, but its subnet mask would place some destinations outside its local subnet, breaking routing to those hosts. APIPA is a fallback that occurs only when no DHCP lease can be obtained, not when the lease has an invalid subnet mask.
When this WOULD be correct
In a scenario where a client receives a valid IP address from DHCP but cannot communicate with devices on other subnets, an incorrect subnet mask would be the likely cause. For example, if a user's computer gets a 192.168.1.10/24 address but the network uses a /16 subnet, the client may not reach the default gateway.
- ✓
The DHCP server is unreachable.
Why this is correct
When a host is configured for DHCP but cannot reach the DHCP server, it self-assigns an APIPA address in the 169.254.0.0/16 range after timing out. The client sends DHCPDISCOVER broadcasts and receives no DHCPOFFER, so it falls back to link-local addressing. This exactly matches the symptom of a computer showing a 169.254.x.x address, indicating the DHCP server is unreachable or not responding.
- ✗
Duplicate IP address on the network.
Why it's wrong here
A duplicate IP address causes an address conflict, typically detected by the client sending ARP probes before using the address. The operating system would still use the duplicate IP (or switch to another state), but it would not revert to APIPA. APIPA is a DHCP failure fallback, not an IP-conflict response, so a duplicate IP would not produce a 169.254.x.x address.
When this WOULD be correct
A user reports intermittent connectivity and an IP conflict error. The technician finds two devices with the same static IP address. The question would ask for the most likely cause of the conflict, making duplicate IP address the correct answer.
- ✗
DNS server misconfiguration.
Why it's wrong here
DNS misconfiguration affects name resolution, not IP address assignment. A client can still obtain a DHCP lease and hold a proper IP even if its DNS server setting is wrong. The symptom of a 169.254.x.x address indicates a failure to get any IP from DHCP, while DNS problems would produce 'name not resolved' errors but the host would still have a valid routable IP.
When this WOULD be correct
A user can access the internet by IP address but not by domain name. The question would state that the client has a valid IP from DHCP and link lights are active, but browsing fails. In that scenario, DNS server misconfiguration is the most likely cause.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 220-1101 exam frequently reuses these exact scenarios with slightly different constraints.
✓The DHCP server is unreachable.Correct answer▾
Why this is correct
When a host is configured for DHCP but cannot reach the DHCP server, it self-assigns an APIPA address in the 169.254.0.0/16 range after timing out. The client sends DHCPDISCOVER broadcasts and receives no DHCPOFFER, so it falls back to link-local addressing. This exactly matches the symptom of a computer showing a 169.254.x.x address, indicating the DHCP server is unreachable or not responding.
✗Incorrect subnet mask.Wrong answer — click to see why▾
Why this is wrong here
The user's IP address (169.254.1.5) is an Automatic Private IP Addressing (APIPA) address, which indicates that the DHCP server is unreachable. An incorrect subnet mask would not cause the client to self-assign an APIPA address; it would typically result in connectivity issues within the subnet but not a 169.254.x.x address.
★ When this WOULD be the correct answer
In a scenario where a client receives a valid IP address from DHCP but cannot communicate with devices on other subnets, an incorrect subnet mask would be the likely cause. For example, if a user's computer gets a 192.168.1.10/24 address but the network uses a /16 subnet, the client may not reach the default gateway.
Why candidates choose this
Candidates may confuse symptoms of DHCP failure with subnet mask issues because both can cause internet connectivity loss. They might think the APIPA address is a result of misconfiguration rather than a DHCP server problem.
✗Duplicate IP address on the network.Wrong answer — click to see why▾
Why this is wrong here
A duplicate IP address would cause a conflict, but the client would still typically receive a valid IP from DHCP, not an APIPA address (169.254.x.x). APIPA addresses are assigned when no DHCP response is received.
★ When this WOULD be the correct answer
A user reports intermittent connectivity and an IP conflict error. The technician finds two devices with the same static IP address. The question would ask for the most likely cause of the conflict, making duplicate IP address the correct answer.
Why candidates choose this
Candidates may confuse symptoms of duplicate IP (connectivity issues) with APIPA addressing, not realizing that APIPA is specifically triggered by DHCP failure, not by IP conflicts.
✗DNS server misconfiguration.Wrong answer — click to see why▾
Why this is wrong here
The user's IP address (169.254.1.5) is an Automatic Private IP Addressing (APIPA) address, which indicates a failure to reach a DHCP server. DNS misconfiguration would not cause the client to obtain an APIPA address; it would typically result in name resolution failures while the client still has a valid IP.
★ When this WOULD be the correct answer
A user can access the internet by IP address but not by domain name. The question would state that the client has a valid IP from DHCP and link lights are active, but browsing fails. In that scenario, DNS server misconfiguration is the most likely cause.
Why candidates choose this
Candidates often confuse symptoms of network connectivity issues; they may think DNS is always the culprit for internet access problems, overlooking that an APIPA address indicates a more fundamental DHCP failure.
Analysis generated from the official 220-1101blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Same concept, more angles
1 more way this is tested on 220-1101
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A technician is setting up a new workstation. After connecting the Ethernet cable, the link light on the NIC and the switch port are solid green. The technician runs ipconfig and sees an IP address of 169.254.3.45 with a subnet mask of 255.255.0.0. The workstation cannot ping the default gateway or any other network devices. Which of the following is the MOST likely cause?
easy- A.The Ethernet cable is faulty
- ✓ B.The DHCP server is unavailable or unreachable
- C.The workstation's subnet mask is incorrect
- D.The NIC driver is corrupted
Why B: The 169.254.x.x address with a /16 subnet mask is an Automatic Private IP Addressing (APIPA) address, assigned by Windows when a DHCP server is unreachable. The solid link lights confirm Layer 1 connectivity is good, so the issue is that the workstation cannot obtain a valid IP from a DHCP server, preventing communication with the default gateway.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1101 exam.