Global Vs. Port-By-Port Pfc Configuration - Lenovo CN4093 Application Manual

Global vs. Port-by-Port PFC Configuration

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PFC requires CEE to be turned on
CEE is turned on, standard flow control is disabled on all ports, and PFC is enabled
on all ports for 802.1p priority value 3. While CEE is turned on, PFC cannot be
disabled for priority value 3. This default is chosen because priority value 3 is
commonly used to identify FCoE traffic in a CEE environment and must be
guaranteed lossless behavior. PFC is disabled for all other priority values by
default, but can be enabled for one additional priority value.
The administrator can also configure PFC on a port-by-port basis. The method
used will typically depend on the following:
Port-by-port PFC configuration is desirable in most mixed environments where

some CN4093 ports are connected to CEE-capable (FCoE) switches, gateways,
and Converged Network Adapters (CNAs), and other CN4093 ports are
connected to non-CEE Layer 2/Layer 3 switches, routers and Network Interface
Cards (NICs).
 Global PFC configuration is preferable in networks that implement end-to-end
CEE devices. For example, if all ports are involved with FCoE and can use the
same SAN and LAN priority value configuration with the same PFC settings,
global configuration is easy and efficient.
 Global PFC configuration can also be used in some mixed environments where
traffic with PFC-enabled priority values occurs only on ports connected to CEE
devices, and not on any ports connected to non-CEE devices. In such cases, PFC
can be configured globally on specific priority values even though not all ports
make use them.
 PFC is not restricted to CEE and FCoE networks. In any LAN where traffic is
separated into different priorities, PFC can be enabled on priority values for
loss-sensitive traffic. If all ports have the same priority definitions and utilize the
same PFC strategy, PFC can be globally configured.
If you want to enable PFC on a priority, do one of the following:
 Create a separate priority group (see
 Move the priority to an existing priority group in which PFC is turned on.
Since there are separate COS queue and ETS configurations, creating a distinct
priority group is preferred.
When configuring ETS and PFC on the switch, perform ETS configuration before
performing PFC configuration.
If two priorities are enabled on a port, the switch sends PFC frames for both
priorities, even if only traffic tagged with one of the priorities is being received on
that port.
Note: When using global PFC configuration in conjunction with the ETS feature
(see "Enhanced Transmission Selection" on page
pause-tolerant traffic (such as lossless FCoE traffic) is assigned priority values
where PFC is enabled. Pausing other types of traffic can have adverse effects on
LAN applications that expect uninterrupted traffic flow and tolerate dropping
packets during congestion. Use PFC globally only if all priority values assigned for
lossless traffic on one or more ports does not carry loss-tolerant traffic on other
ports.
("Turning CEE On or Off" on page
"Priority Groups" on page
296), ensure that only
Chapter 17: FCoE and CEE
282). When
297).
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