control (PFC) allows you to apply pause functionality to specific classes of
traffic on a link instead of all the traffic on the link. PFC applies pause
functionality based on the IEEE 802.1p CoS value. When the switch enables PFC,
it communicates to the adapter which CoS values to apply the pause.
use PFC to provide lossless service to no-drop system classes. PFC implements
pause frames on a per-class basis and uses the IEEE 802.1p CoS value to
identify the classes that require lossless service.
In the switch, each
system class has an associated IEEE 802.1p CoS value that is assigned by
default or configured on the system class. If you enable PFC, the switch sends
the no-drop CoS values to the adapter, which then applies PFC to these CoS
The default CoS
value for the FCoE system class is 3. This value is configurable.
By default, the
switch negotiates to enable the PFC capability. If the negotiation succeeds,
PFC is enabled and link-level flow control remains disabled regardless of its
configuration settings. If the PFC negotiation fails, you can either force PFC
to be enabled on the interface or you can enable IEEE 802.x link-level flow
If you do not enable
PFC on an interface, you can enable IEEE 802.3X link-level pause.
Ensure that pause
no-drop is configured on a class map for link-level pause.
link-level pause is disabled.