Troubleshooting VLANs

First of all, I should mention that the posts on this blog are not in any particular order. Sometimes, I will just grab a random topic in order to study something. This is how my brain works, and I apologize to the orderly-minded people who consider this chaotic.

Second of all, I am assuming that you are already familiar with this subject. I may skip many fundamentals and jump to the meat. That is exactly what I will do today.

Virtual Local Arean Networks (VLANs) are a means of subdividing switches into broadcast domains. Switches are normally collision domains. If you will have several Layer 3 networks on one switch (such as a network for VOIP and a network for Computers), it is wise and often necessary to create VLANs.

To troubleshoot VLANs on a switch, you can use the following commands:
#show vlan brief (lists the vlans and interfaces in each vlan)
#show vlan id x (replace x with the vlan number you are looking at for status.)
#show spanning-tree vlan x (use this to check root id, discover possible loops)