Networks and Connectivity

Information about the whole service
Wi-Fi (KUINS-Air, etc.)
Connection from Off-campus (VPN)
Administration of On-campus Network
Connection to Off-campus Network Services


  1. HOME
  2. Services
  3. Networks and Connectivity
  4. Administration of On-campus Network
  5. Automatic shutdown in loop fault

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, the network switch blocks the port(i.e. LAN outlet) as soon as it detects a loop. And the switch automatically cancels the block after the loop resolved. The Administrators should report the reason of occurance, details of countermeasures, preventive measures.
  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.

Copyright © Institute for Information Management and Communication, Kyoto University, all rights reserved.