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932 Priority Flow Control Commands
addition to the headroom. With two no-drop priorities per interface and
static allocations, there is only about 30 percent of the buffer space available
for normal forwarding behavior.
The effective default behavior on an interface enabled for PFC without a no-
drop priority is that no flow control (legacy or PFC) is enabled. If the user
enables PFC but does not create any no-drop priorities, the interface will not
be lossless.
Changing the drop and no-drop capabilities on an interface, either in flow
control or priority flow control, may require that all ports briefly drop link.
The priority to flow control group cannot be changed while traffic is running.
When 802.3 link flow control is enabled, all priorities are mapped to a single
flow control group. When 802.1Qbb is enabled, the priorities are each
mapped into their own flow control group, where lossless groups have
additional buffer to handle the round trip delay for flow control. In order to
minimize the impact, the link will only be dropped when changing between
802.3 and 802.1Qbb.
Commands in this Chapter
This chapter explains the following commands:
priority-flow-control mode
Use the priority-flow-control mode on command in Datacenter-Bridging
Config mode to enable Priority-Flow-Control (PFC) on an interface. To
disable Priority-Flow-Control, use the no form of the command.
Syntax
priority-flow-control mode on
priority-flow-control mode off
no priority-flow-control mode
priority-flow-control mode
priority-flow-control priority
clear priority-flow-control statistics
show interfaces priority-flow-control
2CSPC4.X8100-SWUM102.book Page 932 Friday, March 15, 2013 8:56 AM