Configuration Guide User guide

FastIron Configuration Guide 47
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Basic port parameter configuration
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 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 devices” on page 49.
Flow control configuration notes
• Auto-negotiation of flow control is not supported on 10 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 ports, the show interface <port> display shows Flow Control is enabled or Flow
Control is 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.
Brocade(config)# no flow-control
To turn the feature back on, enter the flow-control command.
Brocade(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 41.
To disable flow control capability on a port, enter the following commands.