symmetrical-flow-control enable

Enables symmetrical flow control (SFC) globally.
Syntax
symmetrical-flow-control enable[all-priorities]
no symmetrical-flow-control enable
Command Default

SFC is globally disabled.

Parameters
all-priorities
Specifies SFC on all priorities. If you do not specify the all keyword, SFC is enabled only on priorities from 0 through 4. This parameter is optional.
Modes

Global configuration mode

Usage Guidelines

The no form of this restores the default flow-control settings.

Configuring the symmetrical-flow-control enable command enables SFC globally for priorities from 0 through 4 by default and optionally for all priorities from 0 through 7. Using symmetrical-flow-control enable command is recommended as this turns on SFC for priorities from 0 through 4 and does not impact other high priority queues.

Caution: Enabling SFC on all priorities is not recommended as it can cause network instability.

By default, the system runs in tail-drop mode, with all ports honoring 802.3x flow control and disabling 802.3x transmit. The symmetrical-flow-control enable command enables transmission of 802.3x pause frames.

Configuring the symmetrical-flow-control enable command changes priority-to-PG mapping.

You cannot configure the symmetrical-flow-control enable command if the priority-flow-control command is enabled.

If the symmetrical-flow-control enable command is not enabled, you cannot configure the flow-control generate-only or the flow-control both commands in interface configuration mode.

Examples

The following example enables SFC.

device# configure terminal
device(config)# symmetrical-flow-control enable

The following example enables all priorities to send the IEEE 802.3x pause.

device# configure terminal
device(config)# symmetrical-flow-control enable all-priorities

The following example enables SFC for generate-only mode.

device(config)# symmetrical-flow-control enable
device(config)# flow-control generate-only

The following example enables SFC for both honor and generate-only mode.

device(config)# symmetrical-flow-control enable
device(config)# flow-control both
History
Release version Command history
08.0.10 This command was introduced.