Basic Troubleshooting Tips - HP E3800-24G-2SFP+ Installation And Getting Started Manual

Troubleshooting

Basic Troubleshooting Tips

5-2
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
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 switch behaves in this way (in compliance with the IEEE
802.3 standard), if a device connected to the switch has a fixed configu-
ration 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 that all devices connected to the switch 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 or compare your
cable to the cable in appendix B, "Cables and Connectors" for pinouts and
correct cable wiring. A category 5 cable tester is a recommended tool for
every 100Base-TX and 1000Base-T network installation.
Improper Network Topologies. It is important to make sure you have
■
a valid network topology. Common topology faults include excessive
cable length and excessive repeater delays between end nodes. If you have
network problems after recent changes to the network, change back to
the previous topology. If you no longer experience the problems, the new
topology is probably at fault. Sample topologies are shown at the end of
chapter 2 in this book, and some topology configuration guidelines can
be found online at the HP Web site, www.hp.com/networking/support.