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Automatic shutdown in loop fault

  1. Loop fault
    When the circular route (loop) was created by the misconnection, the transmitted data will be kept being forwarded without deleted in the route which eventually fills out the communications bandwidth of the LAN and causes the shutdown of network switch etc.

  2. The shutdown after detecting loop
    To prevent this fault, we shutdown the port(i.e. LAN outlet) as soon as we detected the loop. In some buildings, the latest switches automatically cancel the shutdown after the loop disappeared. As for other buildings, we notice the manager of VLAN by mail. Managers are required to resolve the fialure, report the reason of occurance, the content of measure, the measure for prevention. After confirming the report, shutdown will be cancelled.

  3. Main reasons
    • Both ends of one LAN cable were connected to the two LAN outlet.
    • Both ends of one LAN cable were connected to the HUB to one LAN outlet.
    • Two LAN cables from the separate LAN outlets were connected to one HUB.
    • Two HUB connected to the separate LAN outlets were connected with one LAN cable.

  4. Measures to prevent the loop
    • Attach the tag(destination label) to the both ends of LAN cable and make the connection source and destination clear.
    • HUB has to be set to the easy-to-find place, not behind the shelf, not under the desk.
    • Assign the network manager in your room and understand the network structure. Any change should be approved by the manager.
    • Create the network connection diagram and display it in the readily visible place.
    • Use the HUB with loop detecting function.
 

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