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Troubleshooting Radio Frequency Interference in ExtremeCloud IQ

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TitleTroubleshooting Radio Frequency Interference in ExtremeCloud IQ
Symptoms

Symptoms

  • Slow wireless speeds
  • Frequent disconnections
Environment
  • ExtremeCloud IQ
  • Any HiveOS AP
  • Any HiveOS firmware version
Cause
Resolution

Checking Neighboring Signals

How to SSH in to a device using PuTTY and run the command: show acsp neighbor

  • Columns to pay attention to:

    • Channel
      • This will show the channel the neighboring signal is using.
        • Confirm that the channels are approved channels for your location (1, 6, and 11 for 2.4GHz for the USA, for example).
        • Also confirm that no particular channel is overloaded.
          • If a channel seems to be overused, adjust what channels the APs are using, to more evenly distribute the traffic.
    • RSSI(dBm) 
      • This shows the strength of any neighboring signals. Ideally, this should be between -75 and -100.
      • If signals show in the -50s, -40s, or anything else closer to 0, that signal is overlapping with the signal of this AP, which causes packet damage.
    • Aerohive AP
      • This will indicate if the neighboring signal is coming from an Aerohive device or not.
      • Devices that are Aerohive devices, are likely devices in the same network as this AP, which means adjustments can be made to remedy the issue.
      • Devices that are not Aerohive devices are coming from other wireless networks near by. Devices that aren't Aerohive APs, even if they have a signal that is overlapping with the current AP, we likely won't be able to do anything about.

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Reading the example

  • In the example above, the values to be concerned about are highlighted, all in the -50s RSSI range.
    • Unfortunately they aren't Aerohive devices, so we likely do not have the option to lower the power on these devices.
  • There are also some neighbors on channel 9, which isn't a non-overlapping 2.4GHz channel in the USA (where these examples were taken).

How to fix high RSSI neighbors

  • Go to Manage>Devices
  • Click on the host name of the AP
  • Choose Configure (left hand side menu)
  • Interface Settings
  • Expand Wireless Interfaces
  • Set the Transmission Power to Manual
  • Choose the static power level for the AP
    • To avoid creating sudden dead zones in the network space, best practice recommendation is to adjust the power using these steps:
      • Change the power by 2dBm
      • Push an update out to the APs (delta configuration will work for power changes so no reboot is necessary)
      • Wait about an hour to make sure there are no problem areas with the new settings
      • Pull new tech data to compare RSSI readings
      • Continue to adjust as needed. 
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Checking for Damaged Packets

Run the Command: show int wifi0

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  • Shows information regarding the wifi0 radio, typically the 2.4GHz radio
  • Check the summary state (which should be “Goodâ€� or “Fairâ€�),

    • Summary State meanings:
      • Good
        • CRC errors and TX errors are below 5%, and channel utilization is less than 50%.
      • Fair
        • CRC errors and TX errors are below 10%, and channel utilization is less than 65%.
      • Channel RF Overcrowded
        • Channel Utilization is greater than 65%.
      • High Collision
        • The CRC error rate is 10% or greater.
      • High Tx Error
        • The TX error rate is more than 10%
  • Check the noise floor ratio

    • This should be around -90
    • If it's not, this indicates an unbalanced SNR environment
  • Make sure background scans are getting through

    • The data presented in all the commands listed in this guide is updated when an AP does a background scan.
    • If background scans are missed often, the data we're looking at might be outdated.
  • Check the total utilization percentage

    • We want this to be close to the number of clients connected.
      • So for example, if you have 5 clients connected, anywhere from 1-15% is probably okay, but 50% would be much too high

Reading the example

  • In the example above
    • The summary state is High Collision, indicating a problem.
    • The noise floor is within range, meaning the SNR is likely not a problem.
    • Most background scans have been missed, so the data may not be very current.
    • The total utilization is 27%, with 4 client devices currently connect, indicating a problem.

Run the command: show int wifi0 _count

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  • Check for high percentages, anything above 10% is considered an issue
    • Receiving (RX) retries
    • Transmitting (TX) retires
    • CRC failures
    • Unicast data retries
      • High retires mean the traffic is too damaged to read and has to be resent (retired) at least once, likely more than once, before it is readable and the AP can move on to the next bit of traffic.
      • This leads to wifi slow downs, as the same traffic is repeated over and over instead of moving on to new traffic

Reading the example

  • In the example above
    • 23% rx retry rate means that 23% of the received traffic on this AP is too damaged to read, and had to be resent at least once. 
    • 33% CRC failure means that 33% of the traffic this AP sees fails the Cyclical Redundancy Check, which is another way to measure packet damage. Here again we're seeing 33% of the traffic needing to be resent at least once.
    • 3% tx retry rate means 3% of the transmitted traffic from this AP has to be resent at least once. Since this is under 10%, it's considered negligible and not indicative of a problem.
    • 9% unicast data tx retry rate means that 9% of the unicast data sent by this AP has to be reset at least once. Again, since this is below 10%, it does not indicate a problem.
  • Overall, this example shows heavy interference on the wifi0 radio.

Run the command: show int wifi1

  • Check the same things as "show int wifi0", this time for the 5GHz radio.

Run the command: show int wifi1 _count

  • Check the same things as "show int wifi0 _count", this time for the 5GHz radio.

Run the command: show acsp channel-info detail

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  • Will show us the health of each channel.
  • We want to focus on the channel cost here, the lower the channel cost the better.
  • Note: This command can only take in to account Aerohive APs, so if you are sharing air space with a neighboring network or individual hotspots, this output may not be totally accurate.

Reading the example

  • In the example above
    • Channel 1 has a cost of 12, channel 2 has a cost of 32767
    • Channel 1 is the better choice

Run the command: clear forward count int eth0

Wait 5 minutes, time it if you can

At exactly 5 minutes, run the command: show forward count int eth0

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Divide the incoming LLC packets by the number of seconds between the first command and the second command (300 seconds for 5 minutes) to get the average packet per second count. 

  • We want to see less than 30 packets per second.
  • Over 30 packets per second indicates the network is passing too much traffic
    • If you see more than 30 packets per second, run a packet capture to get a better idea of the traffic on your network.

Recommended Setting Changes

Disable the lower data rates on your SSIDs.

  • This will require a stronger connection between the AP and the client device before a client device can connect to the AP.
  • This will mean that the client device needs to be closer to the AP before connecting.
    • Not only will this reduce the chances of unintentional roaming, but it will also reduce the distance the packets need to travel, which will also reduce collision and interference on your network.
  • Go to Configure
  • Select the network policy
  • Open the SSID
  • Expand Additional Settings
  • Customize Optional Settings (at the end of the page)
  • In the 2.4 GHz 11/bg Rate Setting section, turn 1Mbps-9Mbps to N/A.
  • In the 5.0 GHz 11a Rate Setting section, turn 6 Mbps and 9 Mbps to N/A.

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Radio Profile Settings

  • Check which Radio Profile is in use
  • Go to Monitor
  • Click on the host name of the AP
  • Interface Settings (left hand side menu)
  • Choose either the Wifi0 or Wifi1 tab
  • Radio Profile drop down (if this option isn’t visible, make sure the Radio Status is set to “ONâ€�).
  • To edit this Radio Profile, make a note of the name of the object and then go to Configure
  • Common Objects
  • Radio Profiles
  • Open the object in use.

Wifi0 Radio Profile (typically 2.4GHz)

  • Channel Width

    • Find the Channel Selection section
    • Find Channel Width
    • Set this to less than 80MHz channel width.
      • The larger the channel width, the more overlap we have between channels, and if there is a problem on one channel (RF Interference for instance) it is now shared with all of the channels we are combining.

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Short Guard Interval

  • Find the Enable Short Guard Interval option
    • If this is enabled, please disable it.
      • Short Guard Interval is designed to shorten the time between when we send one packet and when we can send the next one.
        • The problem with this is, if we have an environment with interference, we would just be sending more packets in to a crowded environment faster, increasing the damage we are causing.

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Band Steering

  • This only applies if the wifi0 radio has more interference than the wifi1 (typically 5GHz) radio. 
  • Note: If your network has a lot of legacy devices, this may cause problems with those older devices
    • Expand Optimizing Management Traffic Settings
    • Check the box next to “Enable the steering of clients from the wifi0 to the wifi1 bandsâ€�.
    • Set the Band Steering Mode to “Urge 5 GHz band useâ€�.
      • This will encourage (but not force) clients to connect to the wifi1 radio

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Wifi1 Radio Profile (typically 5GHz)

  • Channel Width

    • Find the Channel Selection section
    • Find Channel Width
    • Set this to less than 80MHz channel width
      • The larger the channel width, the more overlap we have between channels, and if there is a problem on one channel (RF Interference for instance) it is now shared with all of the channels we are combining.
  • Short Guard Interval

    • Find the Enable Short Guard Interval option
      • If this is enabled, please disable it
        • Short Guard Interval is designed to shorten the time between when we send one packet and when we can send the next one.
          • The problem with this is, if we have an environment with interference, we would just be sending more packets in to a crowded environment faster, increasing the damage we are causing.

Push these changes out to your APs.

  • A delta configuration push should be enough so we won't have to interrupt client traffic.
    • Monitor
    • Select the check box next to the AP
    • Update Devices
    • Delta Configuration Update
    • Perform Update

Let these new settings run for about an hour, so we can be sure a background scan has gone through, then run the same commands to check RF interference levels.

Additional notes

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