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8-21
Cisco MDS 9000 Family Troubleshooting Guide, Release 3.x
OL-9285-05
Chapter 8 Troubleshooting Ports
Common Problems with Port Interfaces
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.
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