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Difficulty: Very hardWired and Wireless Network Issues

Match each network troubleshooting symptom on the left with its most likely root cause on the right.

  • A client network adapter displays an IP address of 169.254.44.12 and cannot reach any resources outside the local link.Automatic Private IP Addressing (APIPA) assignment due to an unreachable DHCP server.
  • A Gigabit Ethernet connection establishes a link light, but suffers severe throughput loss and high late collision counts during heavy transfers.Duplex mismatch caused by autonegotiation failure or manual misconfiguration.
  • A mobile workstation repeatedly drops network connection and re-authenticates while moving down a hallway between wireless access points.Inadequate wireless cell overlap or misconfigured roaming aggressiveness thresholds.
  • Wireless devices connected to a 2.4 GHz access point experience severe packet loss whenever a breakroom microwave or Bluetooth headset is in use.Non-802.11 radio frequency (RF) interference operating on the 2.4 GHz ISM band.

Answer

1. 169.254.x.x IP address matches APIPA assignment due to DHCP server unreachability.
2. Late collisions on Ethernet link match Duplex mismatch.
3. Frequent drops while roaming between access points match Inadequate wireless cell overlap or roaming aggressiveness.
4. 2.4 GHz drops near appliances match Non-802.11 RF interference.
Each symptom directly corresponds to a specific OSI Layer 1 or Layer 2 network problem: 169.254.x.x indicates APIPA generated by DHCP unreachability; high late collisions under traffic indicate a duplex mismatch; dropped connections during client movement indicate inadequate wireless coverage overlap; and performance hits near microwaves indicate 2.4 GHz RF interference.

Step-by-Step Solution

1
Analyze the 169.254.44.12 symptom.
Recognize that addresses in the range 169.254.0.1 through 169.254.255.254 are self-assigned by APIPA when DHCP discovery attempts fail.
APIPA allows local link communications but lacks a default gateway to communicate outside the subnet.
2
Analyze the late collisions symptom on Gigabit Ethernet.
Identify that late collisions occur when one side transmits full-duplex ignoring CSMA/CD while the opposing end operates in half-duplex.
Late collisions occur beyond the first 64 bytes of a frame and indicate a mismatch in link duplex settings.
3
Analyze the client disassociations while moving across access points.
Associate the dropped signal with roaming failure due to weak signal overlap between access point coverage cells.
Proper roaming requires sufficient overlap so the client can negotiate connection with the target access point before losing connection to the current one.
4
Analyze the performance drop near microwave ovens and Bluetooth devices on 2.4 GHz.
Identify this as non-802.11 ambient RF interference.
The 2.4 GHz Industrial, Scientific, and Medical (ISM) band is shared by non-Wi-Fi radiation sources like microwaves.

Key Concept

Identifying root causes of common physical and data-link layer issues in wired and wireless networks
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Topics

Wired and Wireless Network Issues

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