Troubleshooting Switches and VLANs

A decade ago, most networks were based on routers and hubs and bridges - shared networks that were relatively easy to troubleshoot. Grab your trusty protocol analyzer, tap into the data flow and the problem soon becomes apparent.

Today, our networks are switched and segmented even further with VLANs. Switches bring a variety of benefits - they're fast - in some cases blindingly fast - and they're reliable and they let each device capture the full capacity of the network when needed.

There is one downside to all this power and flexibility. These switched networks can be a difficult to troubleshoot. If a particular end station or network device simply isn't working, that's relatively easy to determine.

The real problem comes when you get that dreaded call from an end user who utters those four dreaded words: “The network is slow.”

Is it really slow? And if it is slow, what's causing that? How do you figure that out? It isn't as easy as just plugging in that old protocol analyzer any more. It's very difficult to get a real picture of the real traffic flowing over a real switched network. How do you capture the big picture when there are thousands of connections happening in real-time? How do you see into switches and VLANs?

Ideally, the approach should be proactive. Proactive efforts to prevent problems from affecting users include regularly interrogating each switch, and monitoring the quality of traffic on each switch port - just as any other segment would be monitored on a regular basis. Implementing tactics such as monitoring and trending switch port statistics and using tools that allow you see inside switches will take you from a troubleshooting mode to a trouble prevention mode.

Fluke Networks' portable analyzers help you see inside switches. With the OptiView Series III Integrated Network Analyzer and the EtherScope Series II Network Assistant, you'll get vision into switch details and port statistics. Plug in anywhere on the network and you'll instantly see which switch port you're connected to and the average and peak utilization. Discover VLAN configuration, top talkers, trend network traffic or drill down to see interface details.

With the resource links listed on this page, you'll get some valuable insights on ways to troubleshoot and monitor your switched network. You'll learn about techniques you can apply and understand the pros and cons of each, and you'll also find out about tools that can best help you out.