Brocade FastIron Ethernet Switch Administration Guide - Manual (Page 65)

Flow control configuration
Flow control (802.3x) is a QoS mechanism created to manage the flow of data between two full-duplex
Ethernet devices. Specifically, a device that is oversubscribed (is receiving more traffic than it can
handle) sends an 802.3x PAUSE frame to its link partner to temporarily reduce the amount of data the
link partner is transmitting. Without flow control, buffers would overflow, packets would be dropped, and
data retransmission would be required.
All FastIron devices support asymmetric flow control, meaning they can receive PAUSE frames but
cannot transmit them. In addition, FCX and ICX devices also support symmetric flow control, meaning
they can both receive and transmit 802.3x PAUSE frames. For details about symmetric flow control,
refer to
Symmetric flow control on FCX and ICX devices on page 67.
Flow control configuration notes
• Auto-negotiation of flow control is not supported on 10 Gbps and 40 Gbps ports, fiber ports, and
copper or fiber combination ports.
• When any of the flow control commands are applied to a port that is up, the port will be disabled and
re-enabled.
• For 10 Gbps and 40 Gbps ports, the show interface command with the appropriate parameters
shows whether Flow Control is enabled or disabled, depending on the configuration.
• When flow-control is enabled, the hardware can only advertise PAUSE frames. It does not advertise
Asym.
Disabling or re-enabling flow control
You can configure the Brocade device to operate with or without flow control. Flow control is enabled by
default globally and on all full-duplex ports. You can disable and re-enable flow control at the Global
CONFIG level for all ports. When enabled globally, you can disable and re-enable flow control on
individual ports.
To disable flow control, enter the no flow-control command.
device(config)
# no flow-control
To turn the feature back on, enter the flow-control command.
device(config)
# flow-control
Syntax: [no] flow-control
NOTE
For optimal link operation, link ports on devices that do not support 803.3u must be configured with like
parameters, such as speed (10,100,1000), duplex (half, full), MDI/MDIX, and Flow Control.
Negotiation and advertisement of flow control
By default, when flow control is enabled globally and auto-negotiation is ON, flow control is enabled and
advertised on 10/100/1000M ports. If auto-negotiation is OFF or if the port speed was configured
manually, then flow control is not negotiated with or advertised to the peer. For details about auto-
negotiation, refer to
Port speed and duplex mode modification on page 59.
Flow control configuration
FastIron Ethernet Switch Administration Guide 65
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