4Figure 1 Flow control on portsConfigure flow control in TxRx mode on Port B and flow control in Rx mode on Port A:• When congestion occurs on Port C, Switch B buffers frames. When the amount of buffered framesexceeds a certain value, Switch B sends a common Pause frame out of Port B to ask Port A tosuspend sending packets. This Pause frame also tells Port A for how long it is expected to pause.• Upon receiving the common Pause frame from Port B, Port A suspends sending packets to Port B fora period.• If congestion persists, Port B keeps sending common Pause frames to Port A until the congestioncondition is removed.To handle unidirectional traffic congestion on a link, configure the flow-control receive enable commandat one end, and the flow-control command at the other. To enable both ends of the link to handle trafficcongestion, configure the flow-control command at both ends.To enable flow control on an Ethernet interface:Step Command Remarks1. Enter system view. system-view N/A2. Enter Ethernet interfaceview.interface interface-typeinterface-number N/A3. Enable flow control.• Enable TxRx flow control:flow-control• Enable Rx flow control:flow-control receive enableUse either command.By default, Rx flow control is disabledon an Ethernet interface.Configuring link state change suppression on an EthernetinterfaceAn Ethernet interface has two physical link states: up and down. Each time the physical link of aninterface goes up or comes down, the physical layer reports the change to the upper layers, and theupper layers handle the change, resulting in increased overhead.To prevent physical link flapping from affecting system performance, configure link change suppressionto delay the reporting of physical link state changes. When the delay expires, the interface reports anydetected change.Link change suppression does not suppress administrative up or down events. When you shut down orbring up an interface by using the shutdown or undo shutdown command, the interface reports the eventto the upper layers immediately.Link-down event suppression enables an interface to suppress link-down events and start a delay timereach time the physical link goes down. During this delay, the interface does not report the link-downevent, and the display interface brief or display interface command displays the interface state as UP. If
