C
HAPTER
30
| Interface Commands
– 773 –
flowcontrol This command enables flow control. Use the no form to disable flow
control.
SYNTAX
[no] flowcontrol
DEFAULT SETTING
Disabled
COMMAND MODE
Interface Configuration (Ethernet, Port Channel)
COMMAND USAGE
◆ 1000BASE-T does not support forced mode. Auto-negotiation should
always be used to establish a connection over any 1000BASE-T port or
trunk.
◆ Flow control can eliminate frame loss by “blocking” traffic from end
stations or segments connected directly to the switch when its buffers
fill. When enabled, back pressure is used for half-duplex operation and
IEEE 802.3-2002 (formally IEEE 802.3x) for full-duplex operation.
◆ To force flow control on or off (with the flowcontrol or no flowcontrol
command), use the no negotiation command to disable auto-
negotiation on the selected interface.
◆ When using the negotiation command to enable auto-negotiation, the
optimal settings will be determined by the capabilities command. To
enable flow control under auto-negotiation, “flowcontrol” must be
included in the capabilities list for any port
◆ Avoid using flow control on a port connected to a hub unless it is
actually required to solve a problem. Otherwise back pressure jamming
signals may degrade overall performance for the segment attached to
the hub.
EXAMPLE
The following example enables flow control on port 5.
Console(config)#interface ethernet 1/5
Console(config-if)#flowcontrol
Console(config-if)#no negotiation
Console(config-if)#
RELATED COMMANDS
negotiation (774)
capabilities (flowcontrol, symmetric) (771)
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