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Question

Difficulty: MediumWired and Wireless Network Issues

A system administrator is troubleshooting intermittent wireless connectivity and degraded network throughput for users in an open-plan office. A wireless site survey reveals that nearby access points operating on the 2.4 GHz frequency band are configured to use channels 2, 3, and 4. Which of the following is the MOST likely cause of the network performance issue?

  1. Co-channel and adjacent-channel interference caused by overlapping channel selectionAnswer
  2. B
    Failure of the primary DNS server to assign dynamic IP address leases to wireless client devices
  3. C
    Inability of an unmanaged Layer 2 switch to route wireless traffic between separate subnets
  4. D
    Overlooked Ethernet physical interface link light status on the wireless access point host ports

Answer

Co-channel and adjacent-channel interference caused by overlapping channel selection
In the 2.4 GHz wireless spectrum, channels are 22 MHz wide but spaced only 5 MHz apart. The standard non-overlapping channels are 1, 6, and 11. Configuring access points on adjacent channels such as 2, 3, and 4 results in co-channel and adjacent-channel interference, leading to packet retransmissions, reduced throughput, and intermittent client disconnections.

Step-by-Step Solution

1
Analyze the environment and reported symptoms.
Users experience slow wireless speeds and intermittent drops on the 2.4 GHz band where access points use channels 2, 3, and 4.
Understanding the channel plan helps identify radio frequency configuration mistakes.
2
Evaluate 2.4 GHz channel characteristics.
Identify that 2.4 GHz channels are spaced 5 MHz apart but require 22 MHz of bandwidth, meaning only channels 1, 6, and 11 do not overlap.
Using adjacent channels like 2, 3, and 4 causes severe signal collision and degradation.
3
Determine the correct root cause.
Channel overlap interference is identified as the cause of degraded network performance.
Reconfiguring the APs to non-overlapping channels (1, 6, and 11) resolves the interference.

Key Concept

2.4 GHz Wireless Channel Overlap and Interference Troubleshooting
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Topics

Wired and Wireless Network Issues

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