Administrator Guide

To configure PFC and ETS parameters on an interface, you must specify the PFC mode, the ETS bandwidth allocation for a
priority group, and the 802.1p priority-to-priority group mapping in a DCB map. No default PFC and ETS settings are applied to
Ethernet interfaces.
Configuration Notes: PFC and ETS in a DCB Map
The 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 the 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 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 the switch, PFC is enabled 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.
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, when DCB is enabled.
● To ensure no-drop handling of lossless traffic, PFC allows you to configure lossless queues on a port (see Configuring
Lossless Queues).
● When you configure a DCB map with more than the maximum lossless queues configured, 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.
● Configure all the backplane ports of the linecards and RPM0 and RPM1 with same dcb-map configuration.
dcb-map linecard 0 backplane all name
dcb-map linecard all backplane all name
● Dell Networking OS allows you to change the default dot1p priority-queue assignments only if the change satisfies the
following requirements in DCB maps already applied to the interfaces:
○ All 802.1p priorities mapped to the same queue must be in the same priority group.
○ A maximum of four PFC-enabled, lossless queues are supported on an interface.
Otherwise, the reconfiguration of a default dot1p-queue assignment is rejected.
● To ensure complete no-drop service, apply the same PFC parameters on all PFC-enabled peers.
Data Center Bridging (DCB)
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