Information Technology Reference
In-Depth Information
23
CHAPTER
Troubleshooting LAN Switching Environments
The sections in this chapter describe common LAN switch features and offer solutions to some of the
most common LAN switching problems. The following items will be covered:
LAN Switching Introduction
•
General Switch Troubleshooting Suggestions
•
Troubleshooting Port Connectivity Problems
•
Troubleshooting Ethernet 10/100-Mb Half-/Full-Duplex Autonegotiation
•
ISL Trunking on Catalyst 5000 and 6000 Family Switches
•
Example of Configuring and Troubleshooting Ethernet 10/100-Mb Autonegotiation
•
Configuring EtherChannel Switch-to-Switch on Catalyst 4000/5000/6000 Switches
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Using PortFast and Other Commands to Fix End-Station Startup Connectivity Problems
•
Configuring and Troubleshooting IP Multilayer Switching
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Troubleshooting Spanning Tree Protocol and Related Design Considerations
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LAN Switching Introduction
If you are new to LAN switching, then the following sections will take you through some of the main
concepts related to switches. One of the prerequisites to troubleshooting any device is to know the rules
under which it operates. Switches have become much more complex over the last few years as they have
gained popularity and sophistication. The next few paragraphs describe some of the key concepts to
know about switches.
Hubs and Switches
Because of the great demand placed on local-area networks, we have seen a shift from a
shared-bandwidth network, using hubs and coaxial cable, to a dedicated bandwidth network, using
switches. A hub allows multiple devices to be connected to the same network segment. The devices on
that segment share the bandwidth with each other. If it is a 10-Mb hub and six devices are connected to
six different ports on the hub, all six devices would share the 10 Mb of bandwidth with each other. A
100-Mb hub would share 100 Mb of bandwidth among the connected devices. In terms of the OSI model,
a hub would be considered a Layer 1 (physical layer) device. It hears an electrical signal on the wire and
passes it along to the other ports.
