220-1101 Question 147
Single answerAutomatic Private IP Addressing (APIPA)A technician is troubleshooting a Windows laptop that cannot access shared folders or the internet after being connected to the office network. The user reports the laptop worked normally yesterday. Running ipconfig shows the IPv4 address is 169.254.23.81 with a subnet mask of 255.255.0.0 and no default gateway. Other users on the same switch can access network resources normally. Which of the following is the MOST likely cause of this issue?
- A
The laptop was unable to contact a DHCP server and assigned itself an APIPA address
- B
The laptop successfully received a static IP configuration from the DNS server
- C
The router intentionally assigned a loopback address for local network testing
- D
The laptop received a valid public IP address but is blocked by the firewall
Show answer and explanation
Correct answer: A
Explanation
This scenario tests recognition and practical interpretation of APIPA. In Windows, when a network adapter is set to obtain an address automatically and a DHCP lease cannot be obtained, the system may self-assign an address in the 169.254.0.0/16 range with a 255.255.0.0 subnet mask. This behavior is defined for link-local addressing and is commonly seen when there is a DHCP outage, a disconnected cable, a bad switch port, VLAN mismatch, wireless association problem, or a local NIC issue. The lack of a default gateway is a key clue that the host will not be able to reach off-subnet resources such as file servers on other networks or the internet. Best-practice troubleshooting includes checking link status, verifying the client is set for DHCP, using ipconfig /release and ipconfig /renew, testing the cable or wireless connection, and confirming DHCP server availability or relay configuration. Microsoft documentation and standard TCP/IP troubleshooting guidance identify 169.254.x.x addressing as APIPA/link-local behavior when DHCP assignment fails.
- A. Correct.
Correct. An IPv4 address in the 169.254.0.0/16 range with a 255.255.0.0 mask indicates Automatic Private IP Addressing (APIPA). Windows assigns an APIPA address when the client is configured for DHCP but cannot reach a DHCP server. Because APIPA does not provide a default gateway, the system can usually communicate only with other hosts on the same local APIPA segment and cannot reach routed networks or the internet.
- B. Incorrect.
Incorrect. DNS servers do not assign static IP configurations to clients. Static addressing is manually configured by an administrator. Also, a 169.254.x.x address is not evidence of successful addressing from any server; it specifically suggests self-assignment after DHCP failure.
- C. Incorrect.
Incorrect. Loopback addressing is 127.0.0.0/8, most commonly 127.0.0.1, and is used for testing the local TCP/IP stack on the same device. A router does not assign loopback addresses to clients for normal network operation. This option confuses loopback with APIPA.
- D. Incorrect.
Incorrect. Public IPv4 addresses are not in the 169.254.0.0/16 range. The absence of a default gateway is another strong sign this is not a valid routable configuration. A firewall issue would not cause Windows to self-assign an APIPA address.