724-746-5500 | blackbox.com
724-746-5500 | blackbox.com
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LGB5028A User‘s Manual
Appendix B: Troubleshooting
Appendix B. Troubleshooting
B.1 Basic Troubleshooting Tips
Most problems are caused by the following situations. Check for these items first when starting your troubleshooting:
Connecting to devices that have a fixed full-duplex configuration.
The RJ-45 ports are configured as “Auto,” that is, when connecting to the attached devices, the switch will operate in one of two
ways to determine the link speed and the communication mode (half-duplex or full-duplex):
• If the connected device is also configured to Auto, the switch will automatically negotiate both link speed and communication
mode.
• If the connected device has a fixed configuration, for example 100 Mbps, at half or full duplex, the switch will automatically
sense the link speed, but will default to a communication mode of half-duplex.
Because the LGB5028A and LGB5052A switches comply with the IEEE 802.3 standard, if a device connected to the switch has a
fixed configuration at full-duplex, the device will not connect correctly to the switch. The result will be high error rates and very
inefficient communications between the switch and the device.
Make sure all devices connected to the LGB5028A and LGB5052A switches are configured to auto negotiate, or are configured to
connect at half-duplex (all hubs are configured this way, for example).
Faulty or loose cables.
Look for loose or obviously faulty connections. If they appear to be OK, make sure the connections are snug. If that does not
correct the problem, try a different cable.
Non-standard cables.
Non-standard and miswired cables may cause network collisions and other network problems, and can seriously impair network
performance. Use a new, correctly wired cable. For pinouts and correct cable wiring, we recommend using a Category 5 cable
tester for every 100BASE-TX and 1000BASE-T network installation.
Improper network topologies.
Make sure you have a valid network topology. If you switch to a new topology and experience problems, the new topology is
probably at fault. In addition, you should make sure that your network topology contains no data path loops.
Check the port configuration.
A port on your switch may not be operating as you expect because it has been put into a “blocking” state by Spanning Tree,
GVRP (automatic VLANs), or LACP (automatic trunking).
NOTE: Normal operation of the Spanning Tree, GVRP, and LACP features may put the port in a blocking state. Or, the port just
may have been configured as disabled through software.
