It is important to develop a systematic approach for troubleshooting switch related problems. The following steps can assist in isolating a problem on a switched network:

1. Check the physical indications, such as LED status.
2. Start with a single configuration on a switch and work outward.
3. Check the Layer 1 link.
4. Check the Layer 2 link.
5. Troubleshoot VLANs that span several switches.

When troubleshooting, check to see if the problem is a recurring one rather than an isolated fault. Some recurring problems are due to growth in demand for services by workstation ports outpacing the configuration, trunking, or capacity to access server resources. For example, the use of Web technologies and traditional applications, such as file transfer and e-mail, is causing network traffic growth that enterprise networks must handle.

Many campus LANs face unpredictable network traffic patterns that result from the combination of intranet traffic, fewer centralized campus server locations, and the increasing use of multicast applications. The old 80/20 rule, which stated that only 20 percent of network traffic went over the backbone, is obsolete. Internal Web browsing now enables users to locate and access information anywhere on the corporate intranet. Traffic patterns are dictated by where the servers are located and not by the physical workgroup configurations with which they happen to be grouped.

If a network frequently experiences bottleneck symptoms, like excessive overflows, dropped frames, and retransmissions, there may be too many ports riding on a single trunk or too many requests for global resources and access to intranet servers.

Bottleneck symptoms may also occur because a majority of the traffic is being forced to traverse the backbone. Another cause may be that any-to-any access is common, as users draw upon corporate Web-based resources and multimedia applications. In this case, it may be necessary to consider increasing the network resources to meet the growing demand.

Web Links VLAN Tech Notes http://www.cisco.com/en/US/tech/ tk389/tk689/tech_tech_notes_list.html