Fault Symptom
Two devices are directly connected through GE interfaces by optical fibers. The GE interfaces, however,alternate between Up/Down states. The following log messages are displayed:
%Nov 12 11:00:10 2007 RouterA PHY/2/PHY:Slot=2;GigabitEthernet2/0/0: change status to down
%Nov 12 11:00:11 2007 RouterB PHY/2/PHY:Slot=2;GigabitEthernet2/0/0: change status to up
Fault Analysis
1. Run the display interface [ interface-type interface-number ] command in any view on the two interconnected interfaces, and you can find that both interfaces receive CRC error packets. The possible causes are as follows:
a. Data transmission is interfered and error codes occur.
b. The optical power is unstable.
c. The transmit interface on the peer device fails.
d. An error occurs during packet resolution on the local device.
2. Through the preceding log messages, you can find that the two interfaces do not turn Up or Down at the same time.
If auto-negotiation is configured, the interconnected interfaces automatically send negotiation frames afer receiving optical signals. If both interfaces receive negotiation frames, they both go Up. In this troubleshooting case, the two interfaces do not turn Up or Down at the same time, which indicates that one interface receives negotiation frames whereas the other does not receive any. Therefore, it can be inferred that a fault occurs during packet transmission over the link.
Through the preceding analysis, it can be determined that a fault occurs on the transmission link. In this case, the following describes how to locate the fault on the transmission link:
3. Through on-site measurement, it is found that both the receive optical power of the two interfaces is -20db, which meets the optical modules' requirement. Therefore, the possibility of a module or optical fiber fault is ruled out.
4. Check the optical fibers and optical modules for other anomalies. You can find that the fiber end is contaminated.
It can be identified that error codes occur on the receive interface due to contamination of the fiber end.
Procedure
1. After the fiber end is cleaned, the receive interface goes Up.
The fault is thus rectified.
Summary
In the case of long-distance transmission, ensure that the optical fiber is bent at less than 90 degrees, free from damage or contamination, and properly connected.
