D-Link DGS-1520 Emulator - Page 1105

DGS-1520 Series Gigabit Ethernet Smart Managed Switch CLI Reference Guide spanning-tree loop-guard no spanning-tree loop-guard Parameters None. Default By default, this option is disabled. Command Mode Interface Configuration Mode. Command Default Level Level: 12. Usage Guideline This command is only available for physical port and port-channel interface configuration. The STP loop guard feature provides additional protection against Layer 2 forwarding loops (STP loops). An STP loop is created when an STP blocking port in a redundant topology erroneously transitions to the forwarding state. This usually happens because one of the ports of a physically redundant topology (not necessarily the STP blocking port) no longer receives STP BPDUs. In its operation, STP relies on continuous reception or transmission of BPDUs based on the port role. The designated port transmits BPDUs, and the non-designated port receives BPDUs. When one of the ports in a physically redundant topology no longer receives BPDUs, the STP conceives that the topology is loop free. Eventually, the blocking port from the alternate or backup port becomes designated and moves to a forwarding state. This situation creates a loop. Example This example shows how to enable the loop guard mode on port 3. Switch#configure terminal Switch(config)#interface eth1/0/3 Switch(config-if)#spanning-tree loop-guard Switch(config-if)# 1101