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Basic Troubleshooting Tips
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
Because the Switch 2650 behaves in this way (in compliance 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 communi-
cations between the switch and the device.
Make sure that all devices connected to the Switch 2650 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 Procurve web site,
In addition, you should make sure that your network topology contains
no data path loops. Between any two end nodes, there should be only
one active cabling path at any time. Data path loops will cause broadcast
storms that will severely impact your network performance.
For your Switch 2650, if you wish to build redundant paths between
important nodes in your network to provide some fault tolerance, you
should enable Spanning Tree Protocol support on the switch. This
ensures that only one of the redundant paths is active at any time, thus
avoiding data path loops. Spanning Tree can be enabled through the
switch console, the web browser interface, or HP TopTools for Hubs &


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