Cisco MDS-9124 Troubleshooting Guide - Page 197

Chapter 8 Troubleshooting Ports Common Problems with Port Interfaces Send documentation comments to [email protected] Table 8-6 Link Flap Reasons Initiated by a Device Connected to the Switch Port (continued) Reason Rx queue overflow LIP F* received LC port shutdown LIP received B2B OPNy tmo B2B OPNy Ret B2B Cr Loss B2B Description The receive queue overflowed in the queue engine occurred. This can happen under the following conditions: • Improper credit configuration at one or both ends of the link. • A bad link can sometimes result in extra R_RDYs. Check for invalid transmission words at both ends. An loop initialization procedure (LIP) was received. The port shutdown was invoked. Use the show process exception CLI command to check for any other errors. An LIP was received while the Rx queue was not empty. An open circuit on a loop (OPNy) timeout occurred while the Rx queue was not empty. An OPNy was returned while the Rx queue was not empty. Credit loss occurred while the Rx queue was not empty. Viewing Port Counters You can use the show interface counters command to view port counters. Typically, you only observe counters while actively troubleshooting, in which case you should first clear the counters to create a baseline. The values, even if they are high for certain counters, can be meaningless for a port that has been active for an extended period. Clearing the counters provides a better idea of the link behavior as you begin to troubleshoot. Use one of the following commands in EXEC mode to clear all port counters or counters for specified interfaces: • clear counters interface all • clear counters interface The counters can identify synchronization problems by displaying a significant disparity between received and transmitted frames. For example, in the case of a broken fiber, if only the Tx path from the F port to the N port is broken, then the switch interface will still have an operational Rx path and will still obtain bit synchronization from the bit stream received from the N port. The switch port will also be able to recognize an incoming NOS from the N port and reply with an OLS. However, because the transmitted OLS never reaches the N port, the R_T_TOV timer expires. In this scenario, the status of the port will also show Link failure or not connected. The key difference between this case and the no bit synchronization case is that the input and output counts for OLS and NOS increment (as there is bit synchronization but no word synchronization). In such a state, you can check that the Tx path from the switch to the Rx input on the N port interface is properly connected. A faulty transmitter on the switch's SFP or a faulty receiver on the N port's SFP could also cause the issue. OL-9285-05 Cisco MDS 9000 Family Troubleshooting Guide, Release 3.x 8-25