Loop Protect

The Loop Protect feature prevents or short circuits loop formation caused by redundant paths in your network by requiring ports to receive BPDUs (RSTP/MSTP only) on point‐to‐point ISLs before their states are allowed to become forwarding. Further, if a BPDU timeout occurs on a port, its state becomes listening until a new 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 message age expiration, it takes on the role of designated port and 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. It will revert to listening if it stops getting a response. Loop Protect also overrides the port admin setting. This protects against misconfiguration (such as disabling STP on a port using the set spantree portadmin port-string disable command) and protocol failure by the connected bridge. By default, the Loop Protect feature is globally disabled on Extreme Networks switch devices and must be globally enabled to operate on all ports. For configuration information, refer to Understanding and Configuring Loop Protect.