10-14
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
78-11380-12
Chapter 10 Configuring Interface Characteristics
Configuring Ethernet Interfaces
Note We strongly recommend that you do not configure IEEE 802.3z flow control when quality of service
(QoS) is configured on the switch. Before configuring flow control on an interface, make sure to return
to the default QoS settings listed in the “Default Standard QoS Configuration” section on page 29-18.
Flow control can be implemented in two forms, symmetric and asymmetric. The symmetric
implementation is suitable for point-to-point links, and asymmetric is suitable for hub-to-end node
connections, where it is desirable for the hub to pause the end system, but not vice-versa. You use the
flowcontrol interface configuration command to set the interface’s ability to receive and send pause
frames to on, off, or desired. The default flow control state for Gigabit Ethernet ports is receive off and
send desired.
These rules apply to flow control settings on the device:
• receive on (or desired) and send on: Flow control operates in both directions; both the local and the
remote devices can send pause frames to show link congestion.
• receive on (or desired) and send desired: The port can receive pause frames and can send pause
frames if the attached device supports flow control.
• receive on (or desired) and send off: 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 and send on: The port sends pause frames if the remote device supports flow control but
cannot receive pause frames from the remote device.
• receive off and send desired: The port cannot receive pause frames but can send pause frames if the
attached device supports flow control.
• receive off and send 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 about 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.
Beginning in privileged EXEC mode, follow these steps to configure flow control on an interface:
To disable flow control, use the flowcontrol receive off and flowcontrol send off interface configuration
commands.
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 | send} {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 Next Page
Loading...
