stp loop-protection (VSI-LDP-PW view)

Usage Scenario

On a network running STP, a device maintains the status of the root port and blocked port by continually receiving Bridge Protocol Data Units (BPDUs) from the upstream device. If ports cannot receive BPDUs from the upstream device due to link congestion or unidirectional link failures, the device will re-select a root port. Then, the previous root port becomes a designated port and the previous blocked port enters the Forwarding state. As a result, loops may occur on the network.

To prevent network loops, run the stp loop-protection command to configure loop protection. If the root port or the Alternate port cannot receive BPDUs from the upstream device for a long period of time after the loop protection function is enabled, the root port or the Alternate port will send a notification message to the NMS. The root port will enter the Discarding state, and the Alternate port remains in the blocked state and no longer forwards packets. This prevents loops on the network. The root port or Alternate port restores the Forwarding state after receiving BPDUs.

An Alternate port is the backup of the root port. When the root port can normally send and receive BPDUs, the Alternate port is in the blocked state.

Between two interconnected devices on a spanning tree, the device closer to the root bridge is the upstream device of the other device.