With Per VLAN Spanning Tree (PVST) we configure a specific switch to become the root bridge for each VLAN. You can do this with the spanning-tree vlan X root primary command which sets the priority automatically, or you can set the priority manually with the spanning-tree vlan X priority command. A Virtual Local Area Network (VLAN) is a logical grouping that segments a network into smaller broadcast domains. VLANs allow you to separate network devices into distinct groups, even if those devices connect to the same physical switch or to different switches. All vlans exisit on all switches. The root bridge is the elected reference point from which all spanning tree paths are calculated. The vlan command in global configuration mode creates a new VLAN and updates an existing VLAN.
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