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 CIN versions of PFC TLV are supported. DCBx also validates PFC congurations that are received in TLVs
from peer devices. By applying a DCB map with PFC enabled, you enable PFC operations on ingress port trac. To achieve
complete lossless handling of trac, congure 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 congured.
When a DCB input policy with PFC prole is congured or uncongured on an interface or a range of interfaces not receiving any
trac, interfaces with PFC settings that receive appropriate PFC-enabled trac (unicast, mixed-frame-size trac) display
incremental values in the CRC and discards counters. (These ingress interfaces receiving pfc-enabled trac have an egress interface
that has a compatible PFC conguration).
NOTE: DCB maps are supported only on physical Ethernet interfaces.
• To remove a DCB map, including the PFC conguration it contains, use the no dcb map command in Interface conguration
mode.
• To disable PFC operation on an interface, use the no pfc mode on command in DCB-Map conguration mode.
• Trac may be interrupted when you recongure PFC no-drop priorities in a DCB map or re-apply the DCB map to an interface.
• For PFC to be applied, the congured priority trac 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 ow control on the interface using the
flowcontrol rx on tx on command. To delete the DCB map, rst disable link-level ow control. PFC is then
automatically enabled on the interface because an interface is PFC-enabled by default.
• To ensure no-drop handling of lossless trac, PFC allows you to congure lossless queues on a port (see Conguring Lossless
Queues).
• When you congure 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 ow control is already enabled on an interface. You cannot
enable PFC and link-level ow control at the same time on an interface.
• In a switch stack, congure all stacked ports with the same PFC conguration.
• Dell Networking OS allows you to change the default dot1p priority-queue assignments only if the change satises the following
requirements in DCB maps already applied to S6000 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 reconguration 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 an S6000 switch, PFC is globally enabled by default, but not applied on specic 802.1p priorities. To enable PFC on 802.1p
priorities, create a DCB map.
The following prerequisites and restrictions apply when you congure PFC in a DCB map:
• You can enable PFC on a maximum of two priority queues on an interface. Enabling PFC for dot1p priorities congures the
corresponding port queue as lossless.
• You cannot enable PFC and link-level ow control at the same time on an interface.
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Data Center Bridging (DCB)