Setting the MSTP Network Diameter

Context

Any two terminals on a switching network are connected through a specific path along multiple devices. The network diameter is the maximum number of devices between any two terminals. A larger network diameter indicates a larger network scale.

In Figure 1, the STP/RSTP network diameter is 5.

S3-S1-S4-S2-S5
S4-S1-S3-S2-S5

Figure 1 STP/RSTP network diameter

An improper network diameter may cause slow network convergence and affect communication. Run the stp bridge-diameter command to set an appropriate network diameter based on the network scale, which helps speed up convergence. Running this command also allows the switch to calculate the optimal Forward Delay timer value, Hello timer value, and Max Age timer value based on the configured network diameter.

It is recommended that all devices be configured with the same network diameter.

Procedure

Run system-view
The system view is displayed.
(Optional) Run stp process process-id
The MSTP process view is displayed.

Skip this step if you perform configurations in the MSTP process 0.
Run stp bridge-diameter diameter
The network diameter is configured.

By default, the network diameter is 7.

The switch calculates the optimal Forward Delay period, Hello timer value, and Max Age timer value based on the specified network diameter.

RSTP uses a single spanning tree instance on the entire network, meaning that performance deterioration cannot be prevented when the network scale increases. Therefore, the network diameter cannot be larger than 7.