Configuring Pfc And Llc - Cisco nexus 5000 series Cli Configuration Manual

Chapter 1 Configuring QoS
S e n d f e e d b a c k t o n x 5 0 0 0 - d o c f e e d b a c k @ c i s c o . c o m
Configuration Guidelines and Limitations
Switch resources (such as buffers, virtual output queues, and egress queues) are partitioned based on the
default and user-defined system classes. The switch software automatically adjusts the resource
allocation to accommodate the configured system classes.
To maintain optimal switch performance, follow these guidelines when configuring system classes and
policies:
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When configuring Ethernet port channels, note the following guidelines:
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Configuring PFC and LLC

Cisco Nexus 5000 Series switches support PFC and LLC on Ethernet interfaces. The Ethernet interface
can operate in two different modes: FCoE mode or standard Ethernet mode.
If the interface is operating in FCoE mode, the Ethernet link is connected at the server port using a
converged network adapter (CNA). Refer to
configuring PFC and LLC when the interface is operating in FCoE mode.
If the interface is operating in standard Ethernet mode, the Ethernet link is connected at the server port
with a standard Ethernet network adapter (NIC). The network adapter must support DCBX protocol for
PFC or ingress policing to be supported on the interface.
Note You must configure a no-drop Ethernet system class for PFC to operate on Ethernet traffic (PFC will be
applied to traffic that matches the CoS value configured for this class).
Configuring PFC and LLC for standard Ethernet is covered in the following topics:
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If less than four Ethernet classes are defined, up to two of these classes can be configured as no-drop
classes. If more than four Ethernet classes are defined, only one of these classes can be configured
as a no-drop class. The default drop class is counted as an Ethernet class.
If priority flow control is enabled on an Ethernet interface, pause will never be applied to traffic with
a drop system class. PFC does not apply pause to drop classes and the link-level pause feature is
never enabled on an interface with PFC.
All FCoE traffic on an Ethernet interface is mapped to one no-drop system class. By default, this
class is associated with CoS value 3, although you can configure a different value. If you configure
standard Ethernet traffic to use the same CoS value as FCoE, the switch does not apply priority flow
control to the standard Ethernet traffic. This traffic is mapped to the default drop system class.
The CoS value 0 is reserved for the default drop system class. This value cannot be mapped to any
other class.
Service policies configured on port channel interfaces are applied to all members of the port
channel. Service policies configured on individual member interfaces are ignored.
Priority flow control is configured on the individual member interfaces of a port channel. The PFC
configuration must be consistent across all members of the port channel for the port channel to
become operational.
Configuring Priority Flow Control, page 1-8
Configuring IEEE 802.3x Link-Level Flow Control, page 1-8
Chapter 1, "Configuring FCoE"
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
Configuration Guidelines and Limitations
for information about
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