220-1101 Networking Practice Question
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?
⚠ Common exam trap
The trap here is that candidates see a solid link light and assume Layer 1 is fine, but then focus on the incorrect subnet mask or a faulty cable, overlooking that the APIPA address is a direct symptom of DHCP failure.
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 unavailable or unreachable
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.
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 Ethernet cable is faulty
Why it's wrong here
A faulty Ethernet cable—whether due to broken wires, damaged connectors, or exceeding maximum length—usually prevents the NIC and switch from completing the link negotiation, resulting in a dead or flickering link LED and often a "network cable unplugged" notification. Here the solid green link lights on both the workstation and the switch confirm that physical-layer synchronization and electrical continuity are intact, so the cable is not the cause of the APIPA address. Even marginal cabling that passes link negotiation, while able to cause CRC errors, would not single-handedly prevent DHCP discovery, because the workstation can still broadcast and receive at Layer 2.
- ✓
The DHCP server is unavailable or unreachable
Why this is correct
The 169.254.x.x address is an APIPA fallback that Windows assigns when a DHCPDISCOVER broadcast goes unanswered for the full timeout period, so the client effectively has no usable IP configuration from DHCP. Because both link lights are solid, the issue exists above Layer 1—likely a dead or overloaded DHCP server, a misconfigured DHCP scope, an incorrect VLAN assignment that isolates the workstation's broadcast domain from the server, or a rogue DHCP server that offers an invalid lease. This explanation directly accounts for why the client defaults to link-local addressing instead of receiving a routable company address.
- ✗
The workstation's subnet mask is incorrect
Why it's wrong here
While a misconfigured subnet mask could certainly prevent proper routing and communication with hosts on other subnets, the 169.254.0.0/16 address and its 255.255.0.0 mask are forcibly assigned by APIPA when no DHCP response is received—not by a user error or a static misconfiguration. Because APIPA's mask is a symptom rather than an independent failure, correcting the mask would do nothing unless the client still has a 169.254 address; the actual fix is to restore DHCP reachability or assign a valid static IP configuration. The mask becomes irrelevant once the client is in APIPA mode, because the address itself is non-routable and not part of the corporate network.
- ✗
The NIC driver is corrupted
Why it's wrong here
A corrupted NIC driver would often cause the NIC to show errors in Device Manager or prevent the link light from coming on. Since the link light is solid, the driver is likely functioning at Layer 1.
Visual reference
Quick reference
IPv4 Address Class Summary
| Class | First Octet Range | Default Mask | Networks | Hosts per Network |
|---|---|---|---|---|
| A | 1–126 | /8 (255.0.0.0) | 126 | 16,777,214 |
| B | 128–191 | /16 (255.255.0.0) | 16,384 | 65,534 |
| C | 192–223 | /24 (255.255.255.0) | 2,097,152 | 254 |
| D | 224–239 | N/A | Multicast groups | — |
| E | 240–255 | N/A | Reserved / experimental | — |
127.x.x.x is reserved for loopback. Modern networks use CIDR (classless) rather than classful addressing.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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