12-19
Catalyst 2928 Switch Software Configuration Guide
OL-23389-01
Chapter 12 Configuring Interface Characteristics
Configuring Ethernet Interfaces
Note
For interfaces gi0/1 to gi0/16, speed and duplex settings do not apply, as they are only internal
server-facing interfaces. For interfaces 17 to 20, speed and duplex do not apply when they are operating
in SFP module mode. For interfaces gi0/23 and gi0/24, speed and duplex do not apply when configured
for media-type internal. For more information, see the
“Access Ports” section on page 12-2
.
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 2928 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.
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
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.
