Why APIPA Addresses Occur Due to VLAN Isolation
A small office uses a single router as the DHCP server for the 192.168.1.0/24 network. The DHCP scope is configured to issue addresses from 192.168.1.100 to 192.168.1.200. A new employee connects a laptop to an available wall jack and receives an IP address of 169.254.13.57. Other devices in the office are receiving valid IP addresses in the 192.168.1.x range. The technician checks the wall jack and the switch port, and the link light is solid green. Which of the following is the MOST likely cause of this issue?
Quick Answer
The answer is a switch port configured for a VLAN that lacks access to the DHCP server. This is correct because the APIPA address 169.254.13.57 signals that the laptop failed to obtain a DHCP lease, yet the solid link light confirms Layer 1 connectivity and other devices receiving valid 192.168.1.x addresses prove the DHCP server and scope are functional. VLAN isolation blocks the DHCP discover and offer packets at Layer 2 or Layer 3, preventing the handshake even though the physical link is up. On the CompTIA A+ Core 1 220-1101 exam, this scenario tests your ability to distinguish between DHCP exhaustion, faulty cabling, and VLAN misconfiguration—a common trap is assuming a solid link light guarantees full network access. Remember the memory tip: “APIPA means the DHCP handshake didn’t happen, so check the VLAN path, not the cable.”
⚠ Common exam trap
The trap here is that candidates see a solid link light and assume Layer 1/2 are fine, then incorrectly blame the DHCP server or scope exhaustion, overlooking the VLAN segmentation issue that blocks broadcast traffic.
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 switch port is configured for a VLAN that does not have access to the DHCP server
The APIPA address 169.254.13.57 indicates the laptop failed to receive a DHCP lease. Since other devices on the same network are getting valid 192.168.1.x addresses, the DHCP server is functional and the scope is not exhausted. A solid link light confirms Layer 1 connectivity, so the most likely cause is that the switch port is assigned to a VLAN that does not have Layer 3 access to the DHCP server, preventing the DHCP discover/offer handshake from completing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The laptop's network adapter is faulty
Why it's wrong here
A faulty adapter would prevent the link from negotiating, yet the switch port shows solid green, and other devices on the same hardware work. It is tempting because a 169.254 address suggests local connectivity trouble, and adapters are a common failure point, but the link light contradicts this.
- ✓
The switch port is configured for a VLAN that does not have access to the DHCP server
Why this is correct
If the port is assigned to a VLAN without a DHCP server or relay, the laptop cannot receive a DHCP offer and falls back to APIPA. This is common in managed switch environments where VLANs are misconfigured.
- ✗
The DHCP scope is exhausted
Why it's wrong here
The scope ends at .200, and other devices are getting valid IPs, so there are available addresses. Additionally, an exhausted scope would not cause a device to get an APIPA address unless the DHCP server is also unreachable.
- ✗
The router's DHCP service is disabled
Why it's wrong here
Other devices are already leasing addresses from the router's scope, proving the DHCP service is running and enabled. It is tempting because a disabled DHCP server does produce APIPA addresses, and it would be the correct diagnosis if every client on the network showed 169.254 addresses.
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Same concept, more angles
3 more ways 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 small office has a router that provides DHCP services. Several users report that they cannot access the internet, but they can still access shared folders on the local network. The technician checks one user's computer and sees an IP address of 169.254.10.25. Which of the following is the MOST likely cause of the issue?
easy- A.The DNS server is not resolving domain names
- B.The default gateway is misconfigured
- ✓ C.The DHCP server is not responding
- D.A duplicate IP address exists on the network
Why C: The IP address 169.254.10.25 falls within the Automatic Private IP Addressing (APIPA) range (169.254.0.0/16), which Windows assigns when a DHCP discovery broadcast fails to receive a response. Since users can still access local shared folders, local link-layer connectivity is intact, but the lack of a valid DHCP lease means they have no default gateway or DNS server configuration, preventing internet access. The most likely cause is that the DHCP server (the router) is not responding to DHCP requests.
Variation 2. A small office uses a single router that provides DHCP services for the LAN. The router is connected to a switch, and all workstations are connected to the switch. Two workstations (Workstation A and Workstation B) are unable to obtain an IP address from DHCP. They both receive APIPA addresses. Other workstations on the same switch obtain IP addresses and can access the internet. The technician checks the router's DHCP server logs and sees that the pool is not exhausted. Which of the following is the MOST likely cause of the issue?
medium- A.Port security on the switch is limiting the number of MAC addresses per port
- B.The default gateway address is incorrect on the router
- ✓ C.The switch ports used by the affected workstations are assigned to a different VLAN than the router
- D.The DHCP relay agent on the switch is misconfigured
Why C: Workstations A and B are on switch ports configured for a different VLAN than the router. The DHCP Discover broadcasts from these workstations remain in their VLAN and never reach the router's DHCP server. As a result, they fail to obtain an IP address and use APIPA. Other workstations on the correct VLAN get DHCP and internet access. Since the DHCP pool is not exhausted, the issue is isolated to the affected ports, making a VLAN mismatch the most likely cause.
Variation 3. A small office uses a single router that provides DHCP services for the LAN. The router is connected to a managed switch, and 20 workstations are connected to the switch. Two workstations (Workstation A and Workstation B) are unable to obtain an IP address from DHCP. They both receive APIPA addresses (169.254.x.x). Other workstations on the same switch obtain IP addresses and can access the internet. The technician checks the router's DHCP server logs and sees that the pool of available addresses is not exhausted. Which of the following is the MOST likely cause of the issue?
easy- ✓ A.The switch ports for Workstation A and B are configured on a different VLAN that does not have DHCP access
- B.The workstations have static IP addresses configured
- C.The DHCP server is out of leases
- D.The network cables for those workstations are faulty
Why A: If Workstation A and B are on a different VLAN that lacks a DHCP relay agent or a DHCP server configured for that VLAN, their DHCP discovery broadcasts will not reach the DHCP server. The router's DHCP logs show available addresses, ruling out exhaustion. Other workstations on the same physical switch obtain IPs because they are on a correctly configured VLAN. APIPA addresses are assigned when no DHCP response is received, which aligns with VLAN isolation blocking DHCP traffic.
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.