H3C Technologies H3C WX5500E Series Access Controllers - Manual (Page 14)

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• Rx mode—Enables an interface to receive but not send common pause frames.
In Figure 1 , when both Port A and Port B forward packets at 1000 Mbps, Port C is easily congested. To
avoid packet loss, enable generic flow control on Port A and Port B.
Figure 1 Generic flow control application
Configure Port B to operate in TxRx mode and Port A to operate in Rx mode:
• When congestion occurs on Port C, Switch B buffers frames. When the amount of buffered frames
exceeds a certain value, Switch B sends a common pause frame out of Port B to ask Port A to
suspend 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 temporarily stops sending packets to
Port B.
• If congestion persists, Port B keeps sending common pause frames to Port A until the congestion
condition is removed.
To configure generic flow control on an Ethernet interface:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enter Ethernet interface view. interface interface-type
interface-number
N/A
3. Enable flow control.
• Enable TxRx mode flow control:
flow-control
• Enable Rx mode flow control:
flow-control receive enable
Use either command.
By default, generic flow control is
disabled on an Ethernet interface.
Configuring physical state change suppression on an Ethernet
interface
An Ethernet interface has two physical link states: up and down. Each time the physical link of an
interface goes up or comes down, the physical layer reports the change to the upper layers, and the
upper layers handle the change, resulting in increased overhead.
To prevent physical link flapping from affecting system performance, configure link change suppression
to delay the reporting of physical link state changes. When the delay expires, the interface reports any
detected change.
Link change suppression does not suppress administrative up or down events. When you shut down or
bring up an interface by using the shutdown or undo shutdown command, the interface immediately
reports the event to the upper layers.
Link-down event suppression enables an interface to suppress link-down events and start a delay timer
each time the physical link goes down. During this delay, the interface does not report the link-down
event, and the display interface brief or display interface command displays the interface state as UP. If
Port A
Switch A Switch B
Port B
1000Mbps
Port C
100Mbps
1000Mbps
Port D
100Mbps
Switch C