Multiple Instance Spanning-Tree Operation

Overview

Multiple-Instance spanning tree operation (802.1s) ensures that only one active path exists between any two nodes in a spanning-treeinstance. A spanning-tree instance comprises a unique set of VLANs, and belongs to a specific spanning-treeregion. A region can comprise multiple spanning-tree instances (each with a different set of VLANs), and allows one active path among regions in a network. Applying VLAN tagging to the ports in a multiple- instance spanning-tree network enables blocking of redundant links in one instance while allowing forwarding over the same links for non-redundant use by another instance.

For example, suppose you have three switches in a region configured with VLANs grouped into two instances, as follows:

VLANs

Instance 1

Instance 2

10, 11, 12

Yes

No

20, 21, 22

No

Yes

 

 

 

4-4