Virtual Cable Test Considerations

When planning to use Virtual Cable Test (VCT), the following considerations and limitations should be taken into account:

• Avoid using VCT commands in a live network environment. Running VCT commands may cause ports to go up or down and can negatively impact network performance.
• The port where the cable is connected must be enabled when you issue the phy cable-diagnostics tdr command to diagnose the cable. If the port is disabled, the command is rejected.
• VCT requires the Ethernet port speed be configured to the default auto-negotiation speed prior to running the test. VCT does not work on ports with fixed speeds. Run the CLI command speed-duplex auto on the target port to ensure proper port speed for the test.
• Cable length measurement may vary due to different physical layers (PHYs) used across ICX products. The VCT feature should not be used for accurately measuring the length of the cable.
• If the remote pair is set to forced 100 Mbps, any change in Media-Dependent Interface (MDI/Media-Dependent Interface Crossover (MDIX) may cause the device to interpret the Multi-Level Transmit (MLT-3) line code as a reflected pulse. In this case, the device will report a faulty condition.
  Note: In this scenario, it is recommended to run the TDR test a few times, clearing the registers before each test.
• Cat 3 or 4 cables with two or three pairs may fail in one or two of the pairs.
• It is not recommended to run VCT commands when adjacent ports are active.
• Fiber ports and 1G transmit media are not supported.
• Link DOWN ports are not used.
• VCT configurations do not apply to the management port.
• Proper cable standards should be followed to avoid impedance mismatches. Otherwise, signal reflections and performance issues can occur.
• Trunk lines and system-wide configurations are not supported.