Multiple Instance Spanning-Tree Operation

Overview

The logical and physical topologies resulting from these VLAN/Instance groupings result in blocking on different links for different VLANs:

Region “A”: Logical Topology

 

 

 

Switch “A”

 

 

 

Root for Instance 1

 

 

 

VLANs: 10, 11, 12

 

 

 

 

 

 

 

Switch “B”

 

 

 

Switch “C”

Instance 1

 

 

 

Instance 1

 

 

 

VLANs: 10, 11, 12

 

 

VLANs: 10, 11, 12

Path blocked for VLANs in instance 1.

Path blocked for VLANs in instance 2.

Switch “A”

Instance 2

VLANs: 20, 21, 22

Switch “B”

 

 

Switch “C”

Root for Instance 2

 

Instance 2

 

VLANs: 20, 21,

22

 

VLANs: 20, 21, 22

Region “A”: Physical Topology

Path blocked for VLANs in instance 2.

 

 

 

Switch “A”

Root for Instance 1

Switch “B”

Switch “C”

Root for Instance 2

Path blocked for VLANs in instance 1.

Figure 5-1. Example of a Multiple Spanning-Tree Application

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