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Catalyst 3750 MetroSwitch Software Configuration Guide
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Chapter 9 Configuring Interface Characteristics
Configuring Ethernet Interfaces
Configuring IEEE 802.3z Flow Control
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 to stop sending until the condition clears by sending a
pause frame. 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.
Note Catalyst 3750 Metro switch ports are capable of receiving, but not sending, pause frames.
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 flow control settings on the device:
• 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: 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.
Note For details on the command settings and the resulting flow control resolution on local and remote ports,
refer to the flowcontrol interface configuration command in the command reference for this release.
Beginning in privileged EXEC mode, follow these steps to configure flow control on an interface:
To disable flow control, use the flowcontrol receive off interface configuration command.
This example shows how to turn on flow control on a port:
Switch# configure terminal
Switch(config)# interface gigabitethernet1/0/1
Switch(config-if)# flowcontrol receive on
Switch(config-if)# end
Command Purpose
Step 1
configure terminal Enter global configuration mode
Step 2
interface interface-id Enter interface configuration mode and the physical interface to
be configured.
Step 3
flowcontrol {receive} {on | off | desired} Configure the flow control mode for the port.
Step 4
end Return to privileged EXEC mode.
Step 5
show interfaces interface-id Verify the interface flow control settings.
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.
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