Reference Guide

Data Center Bridging (DCB) | 295
• When you configure a DCB map, an error message displays if:
• The PFC dot1p priorities result in more than two lossless queues.
• When you apply a DCB map, an error message displays 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.
• FTOS allows you to change the default dot1p priority-queue assignments only if the change satisfies
the following requirements in DCB maps already applied to S5000 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 an S5000 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. For more information, see DCB Map: Configuration
Procedure.
The following prerequisites and restrictions apply when you configure PFC in a DCB map:
• You can enable PFC on a maximum of two priority queues on an interface. 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.