Flow Control

[jay.lasek]

IS flow-control supported on 3560x switches (WS-C3560X-48PF-S) ? If so, both ways or just in?

[acampbell]

Jay,

Flow control is only supported in the interface RECEIVE direction

Configuring IEEE 802.3x 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 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.

---

Note Catalyst 3750-E or 3560-E Catalyst 3750-X or 3560-X ports can receive, but not send, 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, see the flowcontrol interface configuration command in the command reference for this release.

---

To configure flow control on an interface, follow these steps beginning in privileged EXEC mode:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode
Step 2	interface interface-id	Specify the physical interface to be configured, and enter interface configuration mode.
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.

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