Setting the spanning tree mode

The spanning tree modes include:

• STP mode—All ports of the device send STP BPDUs. Select this mode when the peer device of a port supports only STP.

• RSTP mode—All ports of the device send RSTP BPDUs. A port in this mode automatically transits to the STP mode when it receives STP BPDUs from the peer device. A port in this mode does not transit to the MSTP mode when it receives MSTP BPDUs from the peer device.

• MSTP mode—All ports of the device send MSTP BPDUs. A port in this mode automatically transits to the STP mode when receiving STP BPDUs from the peer device. A port in this mode does not transit to the RSTP mode when receiving RSTP BPDUs from the peer device.

• PVST mode—All ports of the device send PVST BPDUs. Each VLAN maintains a spanning tree. In a network, the amount of spanning trees maintained by all devices equals the number of PVST-enabled VLANs multiplied by the number of PVST-enabled ports. If the amount of spanning trees exceeds the capacity of the network, device CPUs will be overloaded. Packet forwarding is interrupted, and the network becomes unstable. The number of PVST-enabled VLANs supported by the device is 144.

The MSTP mode is compatible with the RSTP mode, and the RSTP mode is compatible with the STP mode.

Compatibility of the PVST mode depends on the link type of a port.

• On an access port, the PVST mode is compatible with other spanning tree modes in all VLANs.

• On a trunk port or hybrid port, the PVST mode is compatible with other spanning tree modes only in VLAN 1.

To set the spanning tree mode: