4
Figure 1
Flow control on ports
Configure 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 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 suspends sending packets to Port B for
a period.
•
If congestion persists, Port B keeps sending common Pause frames to Port A until the congestion
condition is removed.
To handle unidirectional traffic congestion on a link, configure the
flow-control receive enable
command
at one end, and the
flow-control
command at the other. To enable both ends of the link to handle traffic
congestion, configure the
flow-control
command at both ends.
To enable 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 flow control:
flow-control
•
Enable Rx flow control:
flow-control receive enable
Use either command.
By default, Rx flow control is disabled
on an Ethernet interface.
Configuring link 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 reports the event
to the upper layers immediately.
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
