Spanning Tree Loop Protect Commands

This chapter provides detailed information for the spanning tree loop protect set of commands for S- K- and 7100-Series platforms. Spanning tree loop protect functionality includes the display and setting of Spanning Tree Loop Protect parameters, including the global parameters of Loop Protect threshold, window, enabling traps, and disputed BPDU threshold, as well as per port and port/SID parameters. For information about configuring Spanning Tree Loop Protect, refer to Spanning Tree Configuration in the S-, K-, and 7100 Series Configuration Guide.

The Loop Protect feature prevents or short circuits loop formation in a network with redundant paths by requiring ports to receive type 2 BPDUs (RSTP/MSTP) on point-to-point inter-switch links (ISLs) before their states are allowed to become forwarding. Further, if a BPDU timeout occurs on a port, its state becomes listening until a BPDU is received.

In this way, both upstream and downstream facing ports are protected. When a root or alternate port loses its path to the root bridge due to a message age expiration it takes on the role of designated port. It will not forward traffic until a BPDU is received. When a port is intended to be the designated port in an ISL it constantly proposes and will not forward until a BPDU is received, and will revert to listening if it fails to get a response. This protects against misconfiguration and protocol failure by the connected bridge.

By default, the Loop Protect feature is globally disabled on Extreme Networks S- K- and 7100-Series devices and must be globally enabled to operate on all ports. For configuration information, refer to the S-, K-, and 7100 Series Configuration Guide.