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Difficulty: MediumMobile Device Wireless and Network Connectivity

A field employee working at a remote site connects a smartphone to a temporary wireless access point. Although the device shows a active Wi-Fi connection, the user cannot load internal company web applications or reach external network resources. Upon inspecting the IP settings on the smartphone, a technician observes an IP address of 169.254.112.45 with a subnet mask of 255.255.0.0. Which of the following is the most likely cause of this connectivity issue?

  1. The smartphone failed to contact a local DHCP server and automatically generated an APIPA address.Answer
  2. B
    The access point was configured on Wi-Fi channel 2, causing co-channel interference with adjacent 2.4 GHz wireless networks.
  3. C
    The cellular service provider disabled data access because the device IMEI was registered instead of the SIM card IMSI.
  4. D
    The smartphone's secure email client attempted to synchronize incoming messages using unencrypted POP3 over port 443.

Answer

The smartphone failed to contact a local DHCP server and automatically generated an APIPA address.
When an OS is set to receive IP configuration automatically via DHCP but receives no response from a DHCP server (due to server offline status, VLAN misconfiguration, or exhaustion of the IP pool), IPv4 link-local addressing (APIPA) automatically assigns an IP in the 169.254.0.1 through 169.254.255.254 range. Because an APIPA address lacks a default gateway, the mobile device cannot communicate with resources outside the immediate local network segment.

Step-by-Step Solution

1
Analyze the IP address observed on the mobile device.
The IP address 169.254.112.45 belongs to the 169.254.0.0/16 address space.
This specific IPv4 range is reserved by IANA for Automatic Private IP Addressing (APIPA).
2
Identify the mechanism that assigns APIPA addresses.
APIPA is activated when a network client configured for DHCP cannot communicate with or receive an IP lease from an active DHCP server.
The client self-assigns a link-local address to enable communication only with other hosts on the immediate local segment.
3
Determine the root cause of the lack of network and internet access.
Because APIPA addresses are non-routable, the smartphone cannot communicate beyond the local broadcast domain or reach the internet/corporate network.
The inability to reach a DHCP server prevents the device from obtaining a valid gateway address and routable IP address.

Key Concept

APIPA Address Assignment and Mobile DHCP Troubleshooting
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Topics

Mobile Device Wireless and Network Connectivity

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