Users Guide

Configuring PFC in a DCB Map
A switch supports the use of a DCB map in which you configure priority-based flow control (PFC) setting. To
configure PFC parameters, you must apply a DCB map on an interface.
PFC Configuration Notes
PFC provides flow control based on the 802.1p priorities in a converged Ethernet traffic that is received on an
interface and is enabled by default when you enable DCB. As an enhancement to the existing Ethernet pause
functionality, PFC stops traffic transmission for specified priorities (CoS values) without impacting other
priority classes. Different traffic types are assigned to different priority classes.
When traffic congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of the
traffic that needs to be stopped. DCBx provides the link-level exchange of PFC parameters between peer
devices. PFC allows network administrators to create zero-loss links for SAN traffic that requires no-drop
service, while at the same time retaining packet-drop congestion management for LAN traffic.
On a switch, PFC is enabled by default on Ethernet ports (pfc mode on command). You can configure PFC
parameters using a DCB map or the
pfc priority command in Interface configuration mode. For more
information, see Configuring Priority-Based Flow Control.
As soon as you apply a DCB map with PFC enabled on an interface, DCBx starts exchanging information with
a peer. The IEEE802.1Qbb, CEE and CIN versions of PFC TLV are supported. DCBx also validates PFC
configurations that are received in TLVs from peer devices. By applying a DCB map with PFC enabled, you
enable PFC operations on ingress port traffic. To achieve complete lossless handling of traffic, configure PFC
priorities on all DCB egress ports.
When you apply or remove a DCB input policy from an interface, one or two CRC errors are expected to be
noticed on the ingress ports for each removal or attachment of the policy. This behavior occurs because the
port is brought down when PFC is configured. When a DCB input policy with PFC profile is configured or
unconfigured on an interface or a range of interfaces not receiving any traffic, interfaces with PFC settings
that receive appropriate PFC-enabled traffic (unicast, mixed-frame-size traffic) display incremental values in
the CRC and discards counters. (These ingress interfaces receiving pfc-enabled traffic have an egress
interface that has a compatible PFC configuration).
NOTE: DCB maps are supported only on physical Ethernet interfaces.
• To remove a DCB map, including the PFC configuration it contains, use the no dcb map command in
Interface configuration mode.
• To disable PFC operation on an interface, use the no pfc mode on command in DCB-Map
configuration mode.
• Traffic may be interrupted when you reconfigure PFC no-drop priorities in a DCB map or re-apply the
DCB map to an interface.
• For PFC to be applied, the configured priority traffic must be supported by a PFC peer (as detected by
DCBx).
Data Center Bridging (DCB) 265