Addendum

Configuring PFC and ETS in a DCB Map

An S6000 switch supports the use of a DCB map in which you configure priority-based flow control and

enhanced transmission selection settings. To configure PFC and ETS parameters, you must apply a DCB

map on an S6000 interface. This functionality is supported on the S6000 platform.

PFC Configuration Notes

Priority-based flow control (PFC) provides a flow control mechanism based on the 802.1p priorities in

converged Ethernet traffic received on an interface and is enabled by default when you enable DCB. As

an enhancement to the existing Ethernet pause mechanism, 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 an S6000 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 DCB Maps and its Attributes.

NOTE: DCB maps are supported only on physical Ethernet interfaces.

When you configure PFC in a DCB map:

• 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 operation on ingress port traffic. To achieve

complete lossless handling of traffic, configure PFC priorities on all DCB egress ports.

• 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).

• If you apply a DCB map with PFC disabled (pfc off):

• You can enable link-level flow control on the interface (flowcontrol rx on tx on command; see Using

Ethernet Pause Frames for Flow Control). To delete the DCB map, first disable link-level flow control.

PFC is then automatically enabled on the interface because an interface is PFC-enabled by default.

• To ensure no-drop handling of lossless traffic, PFC allows you to configure lossless queues on a port

(see Configuring DCB Maps and its Attributes).

• When you configure a DCB map, an error message displays if:

• The PFC dot1p priorities result in more than two lossless queues.

Data Center Bridging (DCB)