stp enable

• On a complex Layer 2 network, STP/RSTP/MSTP can be configured on devices to prevent or break loops.
• To enable STP/RSTP/MSTP, run the stp enable command. The devices running STP/RSTP/MSTP exchange information to discover loops on the network and block some interfaces to trim the ring topology into a loop-free tree topology. This prevents packet replication and circular propagation and device performance deterioration.
• Spanning tree calculation consumes system resources. Therefore, run the stp disable command to disable STP/RSTP/MSTP on devices or interfaces that do not need to participate in spanning tree calculation.

After STP/RSTP/MSTP is enabled on a ring network, STP/RSTP/MSTP immediately calculates spanning trees on the network. Configurations on a device, such as the device priority, port priority, and port path cost, will affect spanning tree calculation. Any change of the configurations may cause network flapping. Therefore, ensure that basic configurations have been complete before enabling STP/RSTP/MSTP. For example:

• The working mode of the device has been configured using the stp mode { mstp | rstp | stp } command.
• The priority of the device on a spanning tree has been set using the stp priority command
• The priority of an interface on a spanning tree instance has been configured using the stp port priority command.
• The device has been set as the primary root bridge of a spanning tree using the stp root primary command.
• The device has been set as a secondary root bridge of a spanning tree using the stp root secondary command.
• The path cost of an interface on a spanning tree instance has been set using the stp cost cost command.
• If the spanning tree protocol is MSTP, an MST region has been configured using the region-name, instance vlan and revision-level commands.
  Other configurations are completed as required.

• If the undo stp enable or stp disable command is run in the system view, the global STP/RSTP/MSTP function is disabled, which may cause a loop.
• STP/RSTP/MSTP must be enabled on all interfaces that participate in spanning tree calculation. Otherwise, a loop may occur.
• If STP and VPLS multi-homing (VPLS multi-homing enables data packets to be blocked on the backup PE's AC interface, preventing loops) have been deployed, the AC interfaces of both the master and backup PEs may be blocked because the backup PE's AC interface does not block Layer 2 protocol packets.