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The ports in a VLAN are always a subset of the ports in a spanning tree group. A VLAN can include all the ports in a given spanning tree group, and there can be multiple VLANs in a spanning tree group, but a VLAN will never have more ports than exist in the spanning tree group. Because VLANs are always subsets of spanning tree groups, the recommended practice is to plan spanning tree groups and then create VLANs.
In the default configuration, an Accelar 1000 Series routing switch contains a single spanning tree group encompassing all the ports in the switch. For most applications, this configuration is sufficient. However, you can define up to 25 spanning tree groups with each having a unique ID number. The default spanning tree group has ID 1 (STG1).
If a VLAN spans multiple switches, it must be within the same spanning tree group across all switches; that is, the ID of the spanning tree group in which it is defined must be the same across all devices.
Note:
A tagged port can belong to multiple spanning tree groups. On tagged ports, the Bridging Protocol Data Units (BPDUs) for all spanning tree groups with ID other than 1 will be tagged. Not all devices can interpret tagged BPDUs, so interoperability may be an issue.
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