12To do… Use the command… RemarksSet the protective action totake on the interface whena loop is detectedloopback-detection action{ no-learning | semi-block |shutdown }OptionalBy default, a looped interface does notreceive or send packets; the systemgenerates traps and deletes all MACaddress entries of the looped interface.With the shutdown keyword specified, theswitch shuts down the looped ports and settheir physical state to Loop down. When alooped port recovers, you must use the undoshutdown command to restore its forwardingcapability.NOTE:• To use loopback detection on an Ethernet interface, you must enable the function both globally and onthe interface.• To disable loopback detection on all interfaces, run the undo loopback-detection enable command insystem view.• To enable a hybrid or trunk port to take the administratively specified protective action, you must use theloopback-detection control enable command on the port.• When you change the link type of an Ethernet interface by using the port link-type command, the switchremoves the protective action configured on the interface. For more information about the port link-typecommand, seeLayer 2—LAN Switching Command Reference.Setting the MDI mode of an Ethernet interfaceNOTE:Fiber ports do not support the MDI mode setting.You can use both crossover and straight-through Ethernet cables to connect copper Ethernet interfaces.To accommodate these types of cables, a copper Ethernet interface can operate in one of the followingMedium Dependent Interface (MDI) modes:• Across mode• Normal mode• Auto modeA copper Ethernet interface uses an RJ-45 connector, which comprises eight pins, each playing adedicated role. For example, pins 1 and 2 transmit signals, and pins 3 and 6 receive signals. The pinrole varies by the MDI modes as follows:• In normal mode, pins 1 and 2 are transmit pins, and pins 3 and 6 are receive pins.• In across mode, pins 1 and 2 are receive pins, and pins 3 and 6 are transmit pins.• In auto mode, the interface negotiates pin roles with its peer.To enable the interface to communicate with its peer, make sure that its transmit pins are connected to theremote receive pins. If the interface can detect the connection cable type, set the interface in auto MDImode. If not, set its MDI mode by using the following guidelines:
