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airFiber - FCS Errors


This article includes the basic troubleshooting steps for failed Ethernet connections on airFiber devices resulting in FCS errors.

Symptom and Steps to Troubleshoot

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Main Symptom: 

  • FCS Error counter rising on the switch port. 

Symptom Troubleshooting Steps:

FCS errors can be caused by a few different factors:

  • Most commonly, the issue is management frames being sent over the wireless interface.
    • The airFiber team has been working this software issue out and it will be resolved in a future firmware release.
    • Most reports of FCS errors stem from this and this does not affect customer traffic.
  • Failing POE or Ethernet cable, or a low-quality Ethernet cable.
    • Replacing the cable and/or the POE has solved the FCS errors for many customers in the past.
    • Check PoE AC power source.
  • Energy coupled into Ethernet cable from RF or magnetic sources.
    • Is cable located in a high RF environment and shielded/grounded properly?
  • Inline lightning protection devices
    • Bypass the device to determine if the FCS issue is resolved.
  • Failed/failing Ethernet port on the device itself.
    • This is caused by improper grounding practices during the installation and maintenance of the AF24/HD. 

A few things that can help:

1. Following proper ground recommendations. Follow this guide to verify your mast and airFiber is properly grounded: airFiber - How to Ground an airFiber Properly.

2. Reduce the length of the Ethernet run. This can be difficult to overcome; Ubiquiti offers two devices that can help:

3. Install Ferrite choke on both ends of the Ethernet run.

4. If all else fails, replace the radio with a known working radio, and double check cable termination and grounding.

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