Administrator Guide

Type, Length, Value (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 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 MAP, including the PFC and ETS configurations it contains, use the no dcb-map map-
name command in INTERFACE Configuration mode.
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 dcb-map 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 dcb-map with PFC disabled (no pfc mode on):
• You can enable link-level flow control on the interface. To delete the dcb-map, 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 a dcb-map 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 MAP 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 a dcb-map or reapply the dcb-
map to an interface.
NOTE
: All these configurations are available only in PMUX mode and you cannot perform these
configurations in Standalone mode.
How Priority-Based Flow Control is
Implemented
Priority-based flow control provides a flow control mechanism based on the 802.1p priorities in converged
Ethernet traffic received on an interface and is enabled by default. As an enhancement to the existing
Data Center Bridging (DCB) 286