Reference Guide

• In a switch stack, configure all stacked ports with the same PFC configuration.
A DCB input policy for PFC applied to an interface may become invalid if you reconfigure dot1p-queue mapping (refer to
the Create Input Policy Maps section in the Quality of Service (QoS) chapter). This situation occurs when the new dot1p-
queue assignment exceeds the maximum number (2) of lossless queues supported globally on the switch. In this case,
all PFC configurations received from PFC-enabled peers are removed and resynchronized with the peer devices.
Traffic may be interrupted when you reconfigure PFC no-drop priorities in an input policy or reapply the policy to an
interface.
Configuring Lossless Queues
DCB also supports the manual configuration of lossless queues on an interface when PFC mode is turned off and priority
classes are disabled in a DCB input policy applied to the interface.
Prerequisite: A DCB input policy with PFC configuration is applied to the interface with the following conditions:
• PFC mode is off (no pfc mode on).
• No PFC priority classes are configured (no pfc priority priority-range).
The configuration of no-drop queues provides flexibility for ports on which PFC is not needed but lossless traffic should
egress from the interface.
Lossless traffic egresses out the no-drop queues. Ingress dot1p traffic from PFC-enabled interfaces is automatically
mapped to the no-drop egress queues.
1. Enter INTERFACE Configuration mode.
CONFIGURATION mode
interface type slot/port
2. Configure the port queues that will still function as no-drop queues for lossless traffic.
INTERFACE mode
pfc no-drop queues queue-range
For the dot1p-queue assignments, refer to the dot1p Priority-Queue Assignment table.
The maximum number of lossless queues globally supported on the switch is two.
The range is from 0 to 3. Separate the queue values with a comma; specify a priority range with a dash; for
example, pfc no-drop queues 1,3 or pfc no-drop queues 2-3.
The default: No lossless queues are configured.
NOTE: FTOS Behavior: By default, no lossless queues are configured on a port.
A limit of two lossless queues is supported on a port. If the amount of priority traffic that you configure to be paused
exceeds the two lossless queues, an error message displays. Reconfigure the input policy using a smaller number of
PFC priorities.
If you configure lossless queues on an interface that already has a DCB input policy with PFC enabled (pfc mode
on
), an error message displays.
Configuring the PFC Buffer in a Switch Stack
In a switch stack, you must configure all stacked ports with the same PFC configuration. In addition, you must configure
a separate buffer of memory allocated exclusively to a service pool accessed by queues on which priority-based control
flows are mapped.
These PFC-enabled queues ensure the lossless transmission of storage and server traffic. The buffer required for the
PFC service pool is calculated based on the number of ports and port queues used by PFC traffic.
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