Configuring Loop Protection on a Port

On a network running VBST, the switch maintains the root port status and status of blocked ports by receiving BPDUs from an upstream switch. If the switch cannot receive any BPDU from the upstream switch because of link congestion or unidirectional link failures, the switch selects a new root port. The original root port becomes a designated port and the original blocked ports change to the Forwarding state. This switching may cause network loops, which can be mitigated by configuring loop protection.

If the root port or alternate port does not receive BPDUs from the upstream device for a long time, the switch enabled with loop protection sends a notification to the NMS. If the root port is used, the root port enters the Discarding state and becomes the designated port. If the alternate port is used, the alternate port keeps blocked and becomes the designated port. In this case, loops will not occur. After the link is not congested or unidirectional link failures are rectified, the port receives BPDUs for negotiation and restores its original role and status.

An alternate port is the backup of the root port. If a switch has an alternate port, you need to configure loop protection on both the root port and alternate port.

Perform the following operations on the root port and alternate port of the switch.