Summary

Shooting trouble with VLANs is no different from anything else. Always have a methodical plan. Know your devices and how to maneuver the CatOS and IOS. Understand routing and switching processes. Beware of autonegotiation of speed, duplex, trunking, and so on. Create backups. Be prepared for vanishing VLANs if you didn't take the appropriate VTP design up front. Know your VTP modes. Have physical and logical maps handy and use them to help you troubleshoot not only complex end-to-end problems, but simple issues, too. Isolate problem domains. Use your tools.

Many things that used to be performed on routers are now performed on switches with router blades. Although many switches are usable the minute you take them out of the box, they are obviously a little more optimal if configured for the environment. Switching and VLAN targets are still ports and interfaces. Don't assume too much. For example, don't just try another cable or another port; try a known good one.

This chapter reviewed real-world intra- and inter-VLAN communication advantages, disadvantages, and issues. The important topics included addressing, gateways, VTP, routing, and probably the one you recall the best: vanishing VLANs. The next two chapters focus on troubleshooting WAN issues to continue to build your troubleshooting skills.