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Chapter 9
Configuring Interface Characteristics
Configuring IEEE 802.3x Flow Control
IEEE 802.3x flow control enables connected Ethernet ports to control traffic rates during congestion by
allowing congested nodes to pause link operation at the other end. If one port experiences congestion
and cannot receive any more traffic, it notifies the other port by sending a pause frame to stop sending
until the condition clears. Upon receipt of a pause frame, the sending device stops sending any data
packets, which prevents any loss of data packets during the congestion period.
Ports can receive, but not send, pause frames.
Note
You use the flowcontrol interface configuration command to set the interface's ability to receive pause
frames to on, off, or desired. The default state is off.
When set to desired, an interface can operate with an attached device that is required to send
flow-control packets or with an attached device that is not required to but can send flow-control packets.
These rules apply to IEEE 802.3x flow control settings on the device:
•
•
Note
For details on the command settings and the resulting IEEE 802.3x flow control resolution on local and
remote ports, see the flowcontrol interface configuration command in the command reference for this
release.
Beginning in privileged EXEC mode, follow these steps to configure IEEE 802.3x flow control on an
interface:
Command
Step 1
configure terminal
Step 2
interface interface-id
Step 3
no shutdown
Step 4
flowcontrol {receive} {on | off | desired}
Step 5
end
Step 6
show interfaces interface-id
Step 7
copy running-config startup-config
To disable IEEE 802.3x flow control, use the flowcontrol receive off interface configuration command.
This example shows how to enable IEEE 802.3x flow control on a port:
Switch# configure terminal
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# flowcontrol receive on
Switch(config-if)# end
78-17058-01
receive on (or desired): The port cannot send pause frames but can operate with an attached device
that is required to or can send pause frames; the port can receive pause frames.
receive off: IEEE 802.3x flow control does not operate in either direction. In case of congestion, no
indication is given to the link partner, and no pause frames are sent or received by either device.
Purpose
Enter global configuration mode
Specify the physical interface to be configured, and enter
interface configuration mode.
Enable the port, if necessary. By default, UNIs are disabled, and
NNIs are enabled.
Configure the IEEE 802.3x flow control mode for the port.
Return to privileged EXEC mode.
Verify the interface IEEE 802.3x flow control settings.
(Optional) Save your entries in the configuration file.
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
Configuring Ethernet Interfaces
9-17
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