Cisco MDS-9124 Troubleshooting Guide - Page 193
Unexpected Link Flapping Occurs
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Chapter 8 Troubleshooting Ports Common Problems with Port Interfaces Send documentation comments to [email protected] Unexpected Link Flapping Occurs Symptom Unexpected link flapping occurs. When a port is flapping, it cycles through the following states, in this order, and then starts over again: 1. Initializing - The link is initializing. 2. Offline - The port is offline. 3. Link failure or not connected - The physical layer is not operational and there is no active device connection. When troubleshooting unexpected link flapping, it is important to know the following information: • Who initiated the link flap. • The actual link down reason. Be sure to check the HBA, because a faulty HBA can manifest symptoms on the attached switch port. For example, if an Nx port is self-diagnosed as faulty by the HBA driver or firmware, the driver can place the port in optical bypass mode. This results in the receive and transmit paths being internally connected through the port. If this happens, the switch port connected to the faulty device will reach bit and word synchronization with itself. If the port is configured in auto mode, this will cause the port to issue an ELP and to try to initialize as an xE port, even if an end device is physically connected to that interface. In this case, a port reason code of isolation because of ELP failure can be displayed even if an ISL is not present. OL-9285-05 Cisco MDS 9000 Family Troubleshooting Guide, Release 3.x 8-21
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