This object determines how the switch responds when a loop is detected on this port: alert(0) merely notifies the admin, while portbased(1) also takes action against the port itself. An admin picks portbased(1) on production ports so a detected loop automatically shuts the port down, and might use alert(0) on ports where blocking would be too disruptive to attempt without human review. For example, setting this to alert(0) means a detected loop will only generate a loopbackStatusChange notification rather than blocking traffic.