Enabling MSTP

Context

After MSTP multi-process is enabled on the switch, you must enable MSTP in the MSTP process view so that the MSTP configuration can take effect in the MSTP process.

Enabling MSTP on a ring network immediately triggers spanning tree calculation on the network. If basic configurations are not performed on switching devices and interfaces before MSTP is enabled, network flapping may occur upon changes to parameters such as device priority and interface priority.

Procedure

Run system-view
The system view is displayed.
Run stp process process-id
The view of the created MSTP process is displayed.
Run stp enable
MSTP is enabled on the MSTP process of the device.

By default, the MSTP function is enabled on the device.

To prevent the CPU from being affected and faults such as network flapping from occurring, the following lists the recommended maximum number of STP-enabled ports in Up state for different models:

S2720-EI, S5720-LI, S5735-L, S5735S-L, S5735S-L-M, S5720S-LI, S5730-SI, S5730S-EI, S6720-LI, S6720S-LI, S6720-SI, S6720S-SI, S5720I-SI, S5720-SI, S5735-S, S5735S-S, S5735-S-I, and S5720S-SI: 128

S5720-EI: 200

S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S: 256

Follow-up Procedure

If the topology of a spanning tree changes, the forwarding paths to associated VLANs are changed. On the switch, therefore, the ARP entries corresponding to these VLANs need to be updated. MSTP processes ARP entries in either fast or normal mode.

In fast mode, ARP entries to be updated are directly deleted.
In normal mode, ARP entries to be updated are rapidly aged.

The remaining lifetime of ARP entries to be updated is set to 0. The switch rapidly processes these aged entries. If the number of ARP aging probe attempts is not set to 0, ARP implements aging probe for these ARP entries.

In either fast or normal mode, MAC entries are directly deleted.

To specify which mode is used for STP/RSTP convergence, run the stp converge { fast | normal } command in the system view.

By default, the normal MSTP convergence mode is used.

If fast mode is used, ARP entries are frequently deleted. This causes high CPU usage on the device (reaching 100%) and results in frequent network flapping. Therefore, using normal mode is recommended.