Concept Guide

Lossless trac egresses out the no-drop queues. Ingress dot1p trac from PFC-enabled interfaces is automatically mapped to the no-drop
egress queues.
1 Enter INTERFACE Conguration mode.
CONFIGURATION mode
interface interface-type
2 Congure the port queues that will still function as no-drop queues for lossless trac.
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 7. Separate the queue values with a comma; specify a priority range with a dash; for example, pfc no-drop
queues 1,7 or pfc no-drop queues 2-7.
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 congured.
NOTE
: Dell EMC Networking OS Behavior: By default, no lossless queues are congured on a port.
A limit of two lossless queues is supported on a port. If the amount of priority trac that you congure to be paused exceeds the two
lossless queues, an error message displays.
It is the user responsibility to have symmetric PFC congurations on the interfaces involved in a particular PFC-enabled trac-ow to
obtain lossless behavior.
Conguring PFC in a DCB Map
A switch supports the use of a DCB map in which you congure priority-based ow control (PFC) setting. To congure PFC parameters,
you must apply a DCB map on an interface.
PFC Conguration Notes
PFC provides ow control based on the 802.1p priorities in a converged Ethernet trac that is received on an interface and is enabled by
default when you enable DCB. As an enhancement to the existing Ethernet pause functionality, PFC stops trac transmission for specied
priorities (CoS values) without impacting other priority classes. Dierent trac types are assigned to dierent priority classes.
When trac congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of the trac that needs to be
stopped. DCBx provides the link-level exchange of PFC parameters between peer devices. PFC allows network administrators to create
zero-loss links for SAN trac that requires no-drop service, while at the same time retaining packet-drop congestion management for LAN
trac.
On a switch, PFC is enabled by default on Ethernet ports (pfc mode on command). You can congure PFC parameters using a DCB
map or the pfc priority command in Interface conguration mode. For more information, see Conguring Priority-Based Flow Control.
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.
Data Center Bridging (DCB)
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