Configuration manual

By applying a DCB input policy with PFC enabled, you enable PFC operation on ingress port traffic. To

achieve complete lossless handling of traffic, also enable PFC on all DCB egress ports or configure the

dot1p priority-queue assignment of PFC priorities to lossless queues.

To remove a DCB input policy, including the PFC configuration it contains, use the no dcb-input

policy-name command in INTERFACE Configuration mode. To disable PFC operation on an interface,

use the

no pfc mode on command in DCB Input Policy Configuration mode. PFC is enabled and

disabled as the global DCB operation is enabled (dcb enable) or disabled (no dcb enable).

You can enable any number of 802.1p priorities for PFC. Queues to which PFC priority traffic is mapped

are lossless by default. Traffic may be interrupted due to an interface flap (going down and coming up)

when you reconfigure the lossless queues for no-drop priorities in a PFC input policy and reapply the

policy to an interface.

To apply PFC, a PFC peer must support the configured priority traffic (as detected by DCBx).

To honor a PFC pause frame multiplied by the number of PFC-enabled ingress ports, the minimum link

delay must be greater than the round-trip transmission time the peer requres.

If you apply an input policy with PFC disabled (no pfc mode on):

• You can enable link-level flow control on the interface. To delete the input policy, first disable link-

level flow control. PFC is then automatically enabled on the interface because an interface is by

default PFC-enabled.

• PFC still allows you to configure lossless queues on a port to ensure no-drop handling of lossless

traffic.

NOTE: You cannot enable PFC and link-level flow control at the same time on an interface.

When you apply an input policy to an interface, an error message displays if:

• The PFC dot1p priorities result in more than two lossless port queues globally on the switch.

• Link-level flow control is already enabled. You cannot be 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.

A DCB input policy for PFC applied to an interface may become invalid if you reconfigure dot1p-queue

mapping. 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.

Enhanced Transmission Selection

Enhanced transmission selection (ETS) supports optimized bandwidth allocation between traffic types in

multiprotocol (Ethernet, FCoE, SCSI) links.

ETS allows you to divide traffic according to its 802.1p priority into different priority groups (traffic

classes) and configure bandwidth allocation and queue scheduling for each group to ensure that each

traffic type is correctly prioritized and receives its required bandwidth. For example, you can prioritize

low-latency storage or server cluster traffic in a traffic class to receive more bandwidth and restrict best-

effort LAN traffic assigned to a different traffic class.

Data Center Bridging (DCB)