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# About pause flood protection

Ethernet switch interfaces use pause frame-based flow control mechanisms to control data flow. When a pause frame is received on a flow control enabled interface, the transmit operation is stopped for the pause duration specified in the pause frame. All other frames destined for this interface are queued up. If another pause frame is received before the previous pause timer expires, the pause timer is refreshed to the new pause duration value. If a steady stream of pause frames is received for extended periods of time, the transmit queue for that interface continues to grow until all queuing resources are exhausted. This condition severely impacts the switch operation on other interfaces. In addition, all protocol operations on the switch are impacted because of the inability to transmit protocol frames. Both port pause and priority-based pause frames can cause the same resource exhaustion condition.

Virtual Connect interconnects provide the ability to analyze server downlink ports for pause flood conditions and take protective action by disabling the port. Virtual Connect 4.31 and later also monitors and reports on uplinks and stacking links for pause flood. The default polling interval is 10 seconds and is not customer configurable. The SNMP agent supports trap generation when a pause flood condition is detected or cleared.

See also

- Logical Interconnects

- Networks

- Troubleshooting: Pause flood condition detected on a Flex-10 physical port

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