Overview of STP/RSTP
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 making the MAC address table unstable. As a result, network communication may encounter quality deterioration or even interruption. STP solves this problem. STP refers to Spanning Tree Protocol defined in IEEE 802.1D, which develops into Rapid Spanning Tree Protocol (RSTP) in IEEE 802.1w and then Multiple Spanning Tree Protocol (MSTP) in IEEE 802.1S.
MSTP is compatible with RSTP and STP, and RSTP is compatible with STP. Figure 9-2 compares the STP, RSTP, and MSTP protocols.
Spanning Tree Protocol |
Characteristics |
Usage Scenario |
|---|---|---|
STP |
|
All VLANs share one spanning tree, and users or services do not need to be differentiated. |
RSTP |
|
|
MSTP |
|
Traffic in different VLANs is forwarded through different spanning trees for load balancing. The spanning trees are independent of each other. In this situation, users or services are distinguished by VLANs. |
Purpose
After a spanning tree protocol is configured on an Ethernet switching network, the protocol calculates the network topology to implement the following functions:
- Loop prevention: The spanning tree protocol blocks redundant links to prevent potential loops on the network.
- Link redundancy: If an active link fails and a redundant link exists, the spanning tree protocol activates the redundant link to ensure network connectivity.
