Configuring Pfc And Ets In A Dcb Map; Pfc Configuration Notes - Dell S4820T Configuration Manual

Configuring PFC and ETS in a DCB Map

switch supports the use of a DCB map in which you configure priority-based flow control (PFC) and
enhanced transmission selection (ETS) settings. To configure PFC and ETS parameters, you must apply a
DCB map on interface. This functionality is supported on the platform.

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 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
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.
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).
• If you apply a DCB map with PFC disabled (pfc off), you can enable link-level flow control on the
interface using the flowcontrol rx on tx on command. 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 Lossless
• When you configure a DCB map, an error message is displayed if the PFC dot1p priorities result in
more than two lossless queues.
• When you apply a DCB map, an error message is displayed if link-level flow control is already enabled
on an interface. You cannot enable PFC and link-level flow control at the same time on an interface.
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Queues).
Control.
Data Center Bridging (DCB)