220-1101 Question 118
Single answerDHCPA technician is setting up a small office network after replacing the router that provides DHCP services. Several Windows laptops connect to the Wi-Fi successfully, but users cannot access the internet or shared printers. Running ipconfig on one affected laptop shows an IPv4 address of 169.254.42.18 with a subnet mask of 255.255.0.0. Which of the following is the MOST likely cause of the problem?
- A
The DHCP server on the router is disabled or unreachable
- B
The laptop has an incorrect DNS server configured
- C
The default gateway address on the laptop is duplicated on the network
- D
The wireless adapter is negotiating at the wrong speed
Show answer and explanation
Correct answer: A
Explanation
This scenario tests recognition of APIPA behavior and practical DHCP troubleshooting. In Windows, a 169.254.x.x address indicates the client did not receive a valid IPv4 lease from DHCP and assigned itself a link-local address instead. Because multiple devices are affected immediately after replacing the router, the most likely root cause is that the new router's DHCP service is disabled, improperly configured, or not accessible on the network. Best practice is to verify that DHCP is enabled on the router, confirm the scope is configured correctly, and renew the client lease using commands such as ipconfig /release and ipconfig /renew after correcting the issue. This aligns with standard Microsoft documentation on APIPA and common CompTIA A+ troubleshooting methodology for connectivity problems.
- A. Correct.
Correct. An address in the 169.254.0.0/16 range is an Automatic Private IP Addressing (APIPA) address assigned by Windows when the client cannot obtain a lease from a DHCP server. In this scenario, multiple clients are affected after the router replacement, which strongly suggests the DHCP service on the router is turned off, misconfigured, or otherwise unreachable.
- B. Incorrect.
Incorrect. A DNS problem can prevent name resolution, but it does not cause a system to self-assign an APIPA address. A client with a valid DHCP lease could still have internet connectivity issues due to DNS, but the presence of 169.254.x.x indicates failure to obtain normal IP configuration first.
- C. Incorrect.
Incorrect. A duplicate default gateway IP could cause intermittent routing issues, but it would not typically cause clients to receive APIPA addresses. The key symptom here is that the clients are not receiving any DHCP-assigned IPv4 configuration at all.
- D. Incorrect.
Incorrect. Wireless speed or duplex negotiation issues can affect performance, but they do not normally result in a 169.254.x.x address. The laptops are connecting to Wi-Fi, so the more relevant issue is failure to reach a DHCP server after link-layer connectivity is established.