Overview of MSTP
Definition
Generally, redundant links are used on an Ethernet switching network to provide link backup and enhance network reliability. The use of redundant links, however, may produce loops, causing broadcast storms and rendering the MAC address table unstable. As a result, the communication quality deteriorates, and the communication service may even be interrupted. The Spanning Tree Protocol (STP) is introduced to solve this problem.
STP refers to STP defined in IEEE 802.1D, the Rapid Spanning Tree Protocol (RSTP) defined in IEEE 802.1w, and the Multiple Spanning Tree Protocol (MSTP) defined in IEEE 802.1s.
MSTP is compatible with RSTP and STP, and RSTP is compatible with STP. STP, RSTP, and MSTP all prevent broadcast storms and achieve redundancy. Table 10-1 compares STP, RSTP, and MSTP.
Spanning Tree Protocol |
Characteristics |
Usage Scenario |
|---|---|---|
STP |
|
STP or RSTP is used when all VLANs share one spanning tree. In this situation, users or services do not need to be differentiated. |
RSTP |
|
|
MSTP |
|
MSTP is used when traffic in different VLANs is forwarded through different spanning trees that are independent of each other to implement load balancing. In this situation, users or services are distinguished by VLANs. |
Purpose
After a spanning tree protocol is configured on an Ethernet switching network, it calculates the network topology and implements the following functions to remove network loops:
- Loop cut-off: The potential loops on the network are cut off by blocking redundant links.
- Link redundancy: If an active path becomes faulty, a redundant link can be activated to ensure network connectivity.
In addition to the above functions, MSTP also ensures faster convergence than STP and can load balance among multiple VLANs.