Configuring Basic STP/RSTP Functions

STP/Rapid Spanning Tree Protocol (RSTP) is used to block redundant links on the Layer 2 network and trim a network into a loop-free tree topology.

Applicable Environment

On a complex network, loops are inevitable. With the requirement for network redundancy backup, network designers tend to deploy multiple physical links between two devices, one of which is the master and the others are the backup. Loops are likely or bound to occur in such a situation. Loops will cause broadcast storms, thereby exhausting network resources and paralyzing the network. Loops also cause flapping of MAC address tables and thus damages MAC address entries. STP/RSTP can be deployed on a network to eliminate loops. If a loop is detected, STP/RSTP blocks one port to eliminate the loop.

As shown in Figure 1, DeviceA, DeviceB, DeviceC, and DeviceD form a ring network. STP or RSTP is deployed on the ring network to eliminate loops, enhancing reliability of the network.

Figure 1 Diagram of a ring network

If the current device supports STP and RSTP, RSTP is recommended.

Pre-configuration Tasks

Before configuring basic STP/RSTP functions, complete the following task:

Connecting interfaces and setting physical parameters for the interfaces to ensure that the physical status of the interfaces is Up

Configuring the STP/RSTP Mode: Before configuring basic STP/Rapid Spanning Tree Protocol (RSTP) functions, you need to configure the working mode of a device to STP/RSTP. RSTP is compatible with STP.

(Optional) Configuring Device Priorities: Select a device (functioning as a root bridge) from devices for each spanning tree. You can configure the priorities of the devices to preferentially select a root bridge. The lower the numerical value is, the higher priority a device has and the more likely the device will be selected as a root bridge.

(Optional) Configuring the Path Cost for a Port: The STP/Rapid Spanning Tree Protocol (RSTP) path cost determines root port selection. The port from which to the root port costs the least is selected as the root port.

(Optional) Configuring Port Priorities: In each spanning tree, select a designated port for each connection according to the bridge ID, the cost of path and port IDs. The lower the numerical value, the more likely the port on a device becomes a designated port; the higher the numerical value, the more likely the port is to be blocked.

Enabling STP/RSTP: After STP/Rapid Spanning Tree Protocol (RSTP) is enabled, spanning trees are calculated.

Verifying the Basic STP/RSTP Function Configuration: After basic STP/Rapid Spanning Tree Protocol (RSTP) functions are configured, you can view the information such as the port role and port status to check whether the spanning tree calculation is correctly performed.