What is the Difference Between STP, RSTP and MSTP

Date 09/29/2024

This article tells you what STP, RSTP, and MSTP are and their differences so that you can correctly choose the protocol that suits you in the application.

STP, RSTP, and MSTP are vital in maintaining a loop-free topology in the network world. They ensure the reliable operation of Ethernet networks, prevent broadcast storms, and ensure optimal path selection. So what are the differences between these three protocols? In this article, I will explore the definitions and differences of these protocols.

STP, RSTP and MSTP Overview

STP

STP is based on the IEEE 802.1D standard and is designed to prevent loops in Ethernet networks by creating a logical tree structure that covers all devices in the network. It uses a tree topology to disable redundant paths while ensuring a single active path for each network segment. STP uses BPDUs to communicate information about the network topology and port status, and it calculates the shortest path from the switch to the root bridge through the root bridge.

RSTP

RSTP is based on IEEE 802.1W and is an STP evolution designed to address the limitations of STP. It significantly reduces the convergence time of the network after topology changes, making it more suitable for modern networks that require fast recovery. This speed increase is achieved through a more efficient state transition mechanism and a quicker protocol handshake process.

Compared to STP, RSTP reduces the convergence time from minutes to seconds by quickly transitioning ports to forwarding or blocking states. RSTP also introduces new port roles such as standby role and backup role to enhance the protocol's ability to quickly handle network changes. RSTP still uses a more efficient BPDU format and process, which can achieve faster network topology calculation.

MSTP

MSTP is based on IEEE 802.1S, which extends the functions of STP and RSTP and allows multiple spanning trees to exist in the same network. This capability allows different VLANs to be mapped to different spanning trees, thereby optimizing the use of network resources and reducing traffic, with greater flexibility and efficiency.

MSTP enables network administrators to configure independent spanning trees for different VLANs by grouping VLANs into their spanning tree instances, thereby achieving optimized traffic distribution and load balancing. Its main functions include: supporting the creation of multiple spanning trees to more efficiently manage traffic and improve network performance; associating different VLANs with specific spanning tree instances to reduce network congestion and enhance redundancy; and enhancing scalability to adapt to large and complex network environments, allowing different VLANs to independently run their own spanning trees. This flexibility enables MSTP to meet diverse network requirements and improve overall network efficiency.

Advantages of Each Protocol

The main advantage of STP is that it can prevent loops, effectively prevent broadcast storms and loops, and ensure the stability of the network. As a primitive protocol, its configuration is relatively simple and has wide support, so STP can be implemented more easily.

RSTP has fast convergence characteristics, which can control the convergence time within 10 seconds. It also introduces new port states, including discard, learn, and forward, which helps to speed up the convergence process. RSTP can interoperate with STP and can be upgraded in stages in a mixed environment, which is quite flexible.

MSTP supports the creation of multiple spanning tree instances, thereby achieving better load balancing and resource utilization. It can also support multiple VLANs in a single spanning tree instance, which reduces the complexity of managing multiple STP instances. MSTP can also improve traffic management, allowing different VLANs to choose different paths, optimize bandwidth, and reduce congestion.

QSFPTEK provides S7600-48TE4Y2Q that supports STP, RSTP, and MSTP. You can switch and use the required protocol at any time.

The Key Difference Between STP, RSTP, and MSTP

	STP	RSTP	MSTP
Standards	IEEE 802.1D	IEEE 802.1W	IEEE 802.1S
Convergence speed	up to 50 seconds	less than 10 seconds	less than 10 seconds
Port status	Block, listen, learn, forward	Discard, learn, forward	Discard, learn, forward
VLAN support	One instance per VLAN	One instance per VLAN	Multiple instances per VLAN
Traffic forwarding	Through a single path, redundant paths are blocked to prevent network loops	Enhance STP by quickly switching ports to the forwarding state, with faster and more efficient traffic processing	Multiple spanning tree instances can load balance on different paths to optimize traffic forwarding
Scalability	Slow convergence, blocked links, limited scalability	Better scalability than STP, but the entire network only runs a single spanning tree	High scalability, with multiple spanning tree instances, can be optimized for different network segments
Backward compatibility	Compatible with RSTP, but allowed in STP mode when connected to RSTP devices	Compatible with STP, can identify STP devices, and can automatically revert to STP mode	Interoperable with RSTP and STP devices, with all the features of RSTP
Configuration complexity	Simple configuration	Moderate configuration difficulty	Complex configuration difficulty

How to Choose the Right Protocol

In specific applications, we need to consider which protocol to choose from multiple aspects, such as network size, complexity, whether to expand, and the requirements for flexibility.

Due to its simple configuration and limited functions, STP is more suitable for small networks and other environments that require uncomplicated configuration and easy implementation. Such features make it one of the choices for basic network settings.

RSTP is more suitable for medium or large networks that require faster convergence speed and higher performance. It can minimize downtime, ensure network stability, and quickly adapt to topology changes.

MSTP is suitable for networks that need to use multiple VLANs. It can create multiple spanning trees, enhance load-balancing capabilities, and optimize network performance. Such features make it more suitable for large-scale and highly segmented application environments.

Conclusion

Understanding STP, RSTP, and MSTP is crucial in choosing a spanning tree protocol that suits you. Each of them has its advantages and is suitable for different network environments. You can choose the right protocol based on your network size, complexity, and specific needs, which will help optimize network performance and improve management efficiency. If you have more questions about STP protocols, please feel free to contact QSFPTEK's CCIE/HCIE engineers at [email protected].