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Interface Commands
4-147
4
Related Commands
negotiation (4-145)
speed-duplex (4-144)
flowcontrol (4-147)
flowcontrol
32
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
• 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.
Related Commands
negotiation (4-145)
capabilities (flowcontrol, symmetric) (4-146)
32. There are interoperability problems between Flow Control and Head-of-Line (HOL)
blocking for the switch ASIC; Flow Control is therefore not supported for this switch.
Console(config)#interface ethernet 1/5
Console(config-if)#flowcontrol
Console(config-if)#no negotiation
Console(config-if)#