Cisco Nexus 5000 Series Switch CLI Software Configuration Guide, NX-OS 4.0(1a)N1 (OL-16597-01, January 2009)

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31-7
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
OL-16597-01
Chapter 31 Configuring QoS
Configuring PFC and LLC
• 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.
When configuring Ethernet port channels, note the following guidelines:
• 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 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 Chapter 29, “Configuring FCoE” for information about
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:
• Configuring Priority Flow Control, page 31-7
• Configuring IEEE 802.3x Link-Level Flow Control, page 31-8
Configuring Priority Flow Control
By default, Ethernet interfaces negotiate PFC capability with the network adapter using DCBX protocol.
When PFC is enabled, PFC is applied to traffic that matches the CoS value configured for the no-drop
Ethernet class.