VLANs are a feature of ethernet switches which makes them act like multiple "virtual switches". Each VLAN is a separate broadcast domain and could be configured with a separate subnet. That way could could have separate subnets for separate purposes (IT, accounting, network management) on one physical switch. This saves money and cabling while decreasing complexity.Spanning tree is a protocol which allows you to build redundant loops out of ethernet switches without suffering a bandwidth outage due to looping ethernet frames. Spanning tree blocks ports in your switch mesh to change a topology of loops into a non-looping tree. Then if you suffer a link outage, spanning tree will reconverge in a new fully operational tree. This reconvergence make take significant time (30-50 seconds) with the old spanning tree protocol.More modern improvements to the spanning tree protocol, including RSTP (rapid spanning tree) and MST (multiple spanning tree) will be covered in a later episode.
