Example 1: Configuring MSTP for Traffic Segregation

This example illustrates the use of MSTP for traffic segregation by VLAN and SID. Bridges A, B, C and D participate in VLAN 10. Bridges A, B, E and F participate in VLAN 20. Traffic Segregation in a Single STP Network Configuration shows the problem that arises when using a single Spanning Tree configuration for traffic segregation with redundancy.

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Traffic Segregation in a Single STP Network Configuration
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In a single Spanning Tree configuration a bridge can only have one port forwarding towards the root for all traffic. Bridge A has the lowest priority and is the root. Bridge B forwards traffic towards the root on port ge.1.2. All other ports are blocked. For this configuration, Bridge B will not have any active links forwarding for VLAN 20.

Traffic Segregation in an MSTP Network Configuration shows the solution using MSTP. By configuring separate Spanning Tree instances to overlay the two VLAN topologies, Bridge B port ge.1.2 forwards on VLAN 10 for SID 1 and port ge.1.3 forwards on VLAN 20 for SID 2.

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Traffic Segregation in an MSTP Network Configuration
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To configure the traffic segregation MSTP example on all bridges:

To configure Bridge A as root, set the priority to 4096 for both SID 1 and SID 2.

set spantree priority priority sid

To configure Bridge B as the backup should Bridge A fail: