Changing The Negotiation Mode; Disabling Or Re-Enabling Flow Control; Specifying Threshold Values For Flow Control - Dell PowerConnect B-RX Configuration Manual

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Disabling or re-enabling flow control

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Unless the ports at both ends of a Gigabit Ethernet link use the same mode (either auto-gig or
neg-off), the ports cannot establish a link. An administrator must intervene to manually configure
one or both sides of the link to enable the ports to establish the link.

Changing the negotiation mode

To change the mode for individual ports, enter commands such as the following.
BigIron RX(config)# int ethernet 4/1 to 4/4
BigIron RX(config-mif-4/1-4/4)# gig-default neg-off
This command changes the default auto-gig setting and sets the negotiation mode to neg-off for
ports 4/1 – 4/4.
Syntax: gig-default neg-full-auto | auto-gig | neg-off
Default is gig-default auto-gig
The neg-full-auto, auto-gig, and neg-off options are as described above.
Disabling or re-enabling flow control
You can configure full-duplex ports on a system to operate with or without flow control (802.3x).
Flow control is enabled by default.
To disable flow control on full-duplex ports on a system, enter the following.
BigIron RX(config)# no flow-control
To turn the feature back on.
BigIron RX(config)# flow-control
Syntax: [no] flow-control

Specifying threshold values for flow control

The 802.3x flow control specification provides a method for slowing traffic from a sender when a
port is receiving more traffic than it can handle. Specifically, the receiving device can send out
802.3x PAUSE frames that request that the sender stop sending traffic for a period of time.
The device generates 802.3x PAUSE frames when the number of buffers available to a module's
Buffer Manager (BM) drops below a threshold value. A module's BM can start running out of
buffers when a port receives more traffic than it can handle. In addition, the device drops the
lowest priority traffic when the number of available buffers drops below a second threshold. When
the number of available buffers returns to a higher level, the device sends out another PAUSE
frame that tells the sender to resume sending traffic normally. You can specify values for both
thresholds, as well as the module where the thresholds are to take effect.
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auto-gig – The port tries to performs a negotiation with its peer port to exchange capability
information. This is the default state.
neg-off – The port does not try to perform a negotiation with its peer port.
BigIron RX Series Configuration Guide
53-1001986-01