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Difficulty: MediumIP Addressing and Network Configuration

A helpdesk technician is troubleshooting a newly connected computer in a satellite office that cannot reach local network shares or internet websites. Running `ipconfig /all` on the client workstation reveals an IPv4 address of 169.254.112.85, a subnet mask of 255.255.0.0, and an empty default gateway entry. Which of the following is the most likely cause of this issue?

  1. The client workstation was unable to contact a DHCP server and automatically configured a Link-Local (APIPA) address.Answer
  2. B
    The local DNS server assigned a temporary fallback address because hostname resolution requests timed out.
  3. C
    The workstation successfully established a static APIPA lease provisioned directly by the default gateway router.
  4. D
    An unmanaged Layer 2 switch blocked IP lease traffic because port 443 was closed on the workstation.

Answer

The client workstation failed to communicate with a DHCP server and automatically self-assigned an Automatic Private IP Addressing (APIPA) address in the 169.254.0.0/16 network block.
When a client computer set to obtain an IP address automatically cannot contact a DHCP server, Windows assigns a self-generated APIPA address in the 169.254.0.0/16 range. This allows basic communications with other hosts on the same local segment but leaves the default gateway unconfigured.

Step-by-Step Solution

1
Analyze the output from the `ipconfig /all` command.
The IPv4 address is identified as 169.254.112.85 with a subnet mask of 255.255.0.0.
Recognizing the address range identifies the mechanism responsible for network address configuration.
2
Evaluate the identified IP address space against standard IPv4 allocation mechanisms.
Addresses starting with 169.254.x.x fall into the APIPA (Link-Local) IPv4 address range reserved by IANA.
APIPA is triggered automatically by host client operating systems when DHCP server requests (DHCPDISCOVER) yield no response.
3
Determine the root cause of the missing default gateway and local network access.
Because APIPA only allows communications within the local broadcast domain and does not assign a default gateway, external and routed subnet communication fails.
Unreachability of the DHCP server prevents standard IP parameter assignment (IP, subnet mask, default gateway, and DNS).

Key Concept

Automatic Private IP Addressing (APIPA / Link-Local IPv4)
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Topics

IP Addressing and Network Configuration

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