The Ultimate Guide to Multiple Spanning Tree Protocol

Introduction

MSTP or Multiple spanning tree protocol is based on IEEE 802.1s standard. MSTP is a protocol which maps multiple VLANs to a single instance.
Before MSTP, normal STP 802.1d or Rapid STP 802.1 which maps single vlan to a single STP instance. MSTP uses the rapid spanning tree protocol features
such as fast convergence, port states, port roles, edge ports and link types. However, with these functionalities, MSTP has also added some new features like regions, instances and mapping.

Lab diagram for Multiple Spanning Tree Protocol

Below is the lab diagram for multiple spanning-tree protocol;

• Configure the hostname of each switch as SW1, SW2, and SW3
• Set the domain vtp mode as server and domain name as “marwat”
• Establish a trunk link among all three switches

Create 15 vlans from vlan 6 to vlan 20 at switch 1.

Check the trunk links of all the switches below;

MSTP Configuration

We will define each MST command in the screenshots below. Go to global configuration mode and configure spanning-tree mode as most.

Enter into mst configuration through the following command

Assign name to the mst region;

Set the revision number from 0 to 4094;

Map the VLANs from 6 to 12 with MST instance. There were 16 multiple spanning tree instances in the old IOS, but now it supports 4095 instances. It is the first mst instance on the switch.

Create another instance 2 and map vlans from 13 to 20.

The next step is to create primary and secondary roots, for instance 1 and instance 2.

Now configure multiple spanning tree protocols on the switch2 and switch.

Now check how many instances are running on the switch.

Three instances are running on the switch which are mst 0, 1, and 2. Those vlans that we didn’t map to any MST instance are included in the MST 0. While we configure Vlans for MST 1 and MST2.

Now run another command “show spanning-tree mst 0” to check MSt 0 instance on switch1;

Similarly, check Multiple spanning-tree 0, 1, and 2 on switch2;

While at the last check on Switch3;