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Understanding flow control

About flow control  Top

Flow control is the management of the flow of frames between two directly connected link-partners. Flow control is achieved by specifying a flow control option that causes packets called Pause frames to be used as needed. For example, a link-partner A sends a Pause On frame to link-partner B when its receive buffers are nearly full. The link-partner B suspends transmission until it receives a Pause Off frame from the link-partner A or a specified timeout threshold is reached. Thus, flow control can reduce or eliminate dropped packets due to overrun.

What the flowcontrol option is used for  Top

Flow control can be configured for the following interfaces:

This configured flow control setting is advertised during autonegotiation. If autonegotiation succeeds, the operational flow control setting is determined based on the negotiated speed and the value advertised by the other device. If autonegotiation fails, the configured flow control setting is used.

Flow control types  Top

The following table describes the types you can specify for the flowcontrol option.

Flow control value

Description

none

No flow control

receive

Ability to receive flow control frames

send

Ability to send flow control frames

full

Ability to send and receive flow control frames

How to configure and view flow control  Top

See Configuring network interfaces for information on configuring and displaying flow control settings. You can also use the ifstat command to view the operational flow control setting. If you do not specify the flowcontrol option when configuring a network interface, the configured flow control setting defaults to full.

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