Loopback Violation
Description
An Access Violation: Loopback Violation may occur when frames are looped on the port and a MAC learned downstream is seen as the source MAC on an upstream packet.
The following is an example of Access Violation: Loopback Violation alarm:
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Note: The source MAC simply indicates the "victim" of the looped packet as this is a packet being looped back to its source. It is given as a troubleshooting hint, but the loop is in the opposite direction of the source MAC. |
Trouble Clearing
The possible causes of the Loopback Violation are:
- Looped Port Downstream of ONT UNI: While Tellabs specifically recommends against attaching switches to ONT UNI ports, if a port of an attached switch is looped, it may end up looping traffic back to the OLT.
- Ensure that STP is on for the downstream switch.
- Enable STP with BPDU Guard and Root Protect
- Ensure that Auto Disable is set in the profile with a suitable timeout.
- OIU8 will automatically detect this.
- See AppNote on this subject: Access Violations and Auto Disable
- Bad Docking Station: It has been observed that some docking stations actually loop traffic when they are booting. This can result in looped packets. This can be resolved as follows:
- Remove the docking station from the system or upgrade to a docking station that does not loop packets.
- Looped Uplink Port: Newer releases send the Loopback packet out of the OIU8 uplink ports and a loop will be detected on the uplink. Consult the information in the alarm to determine the source of the looped packet. SR31.3_603105 was the first release with this feature. Alarms will be signaled against the OIU8 slot which indicates this is a loop on the Uplink of the OLT.
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