Introduction to STP/RSTP
Definition
Redundant links are used on an Ethernet switching network to implement 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 be interrupted. STP solves this problem.
Devices running STP exchange STP bridge protocol data units (BPDUs) to discover loops on the network and block some ports. This ensures a loop-free tree network and that the packet processing capabilities of switches is not impacted.
The STP network convergence speed is slow, so IEEE introduced RSTP (802.1w) in 2001 to improve the network convergence speed of STP.
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.