Users Guide

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 CINIEEE802.1Qbb and CEE 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).
● 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 Queues).
● 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.
● In a switch stack, configure all stacked ports with the same PFC configuration.
● Dell EMC 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 two 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.
PFC Prerequisites and Restrictions
On a switch, PFC is globally enabled by default, but not applied on specific 802.1p priorities. To enable PFC on 802.1p priorities,
create a DCB map.
The following prerequisites and restrictions apply when you configure PFC in a DCB map:
● You can enable PFC on a maximum of twofour priority queues on an interface. The default is two. Enabling PFC for dot1p
priorities configures the corresponding port queue as lossless.
● You cannot enable PFC and link-level flow control at the same time on an interface.
Data Center Bridging (DCB)
255