C613-50100-01 REV C Command Reference for x930 Series 445
AlliedWare Plus™ Operating System - Version 5.4.6-1.x
SWITCHING COMMANDS
BACKPRESSURE
backpressure
Overview This command provides a method of applying flow control to ports running in half
duplex mode. The setting will only apply when the link is in the half-duplex state.
You can disable backpressure on an interface using the off parameter or the no
variant of this command.
Syntax
backpressure {on|off}
no backpressure
Default Backpressure is turned off by default. You can determine whether an interface has
backpressure enabled by viewing the running-config output; backpressure on is
shown for interfaces if this feature is enabled.
Mode Interface Configuration
Usage The backpressure feature enables half duplex Ethernet ports to control traffic flow
during congestion by preventing further packets arriving. Back pressure utilizes a
pre-802.3x mechanism in order to apply Ethernet flow control to switch ports that
are configured in the half duplex mode.
The flow control applied by the flowcontrol (switch port) command operates only
on full-duplex links, whereas back pressure operates only on half-duplex links.
If a port has insufficient capacity to receive further frames, the device will simulate
a collision by transmitting a CSMACD jamming signal from this port until the buffer
empties. The jamming signal causes the sending device to stop transmitting and
wait a random period of time, before retransmitting its data, thus providing time
for the buffer to clear. Although this command is only valid for switch ports
operating in half-duplex mode the remote device (the one sending the data) can
be operating in the full duplex mode.
To see the currently-negotiated duplex mode for ports whose links are up, use the
command show interface. To see the configured duplex mode (when different
from the default), use the command show running-config.
Examples To enable back pressure flow control on interfaces port1.0.1-port1.0.2
enter the following commands:
awplus# configure terminal
awplus(config)# interface port1.0.1-port1.0.2
awplus(config-if)# backpressure on
Parameters Description
on Enables half-duplex flow control.
off Disables half-duplex flow control.
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