Concept Guide
Lossless trac egresses out the no-drop queues. Ingress dot1p trac from PFC-enabled interfaces is automatically mapped to the no-drop
egress queues.
1 Enter INTERFACE Conguration mode.
CONFIGURATION mode
interface interface-type
2 Congure the port queues that will still function as no-drop queues for lossless trac.
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 congured.
NOTE
: Dell EMC Networking OS Behavior: By default, no lossless queues are congured on a port.
A limit of two lossless queues is supported on a port. If the amount of priority trac that you congure to be paused exceeds the two
lossless queues, an error message displays.
It is the user responsibility to have symmetric PFC congurations on the interfaces involved in a particular PFC-enabled trac-ow to
obtain lossless behavior.
Conguring PFC in a DCB Map
A switch supports the use of a DCB map in which you congure priority-based ow control (PFC) setting. To congure PFC parameters,
you must apply a DCB map on an interface.
PFC Conguration Notes
PFC provides ow control based on the 802.1p priorities in a converged Ethernet trac 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 trac transmission for specied
priorities (CoS values) without impacting other priority classes. Dierent trac types are assigned to dierent priority classes.
When trac congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of the trac 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 trac that requires no-drop service, while at the same time retaining packet-drop congestion management for LAN
trac.
On a switch, PFC is enabled by default on Ethernet ports (pfc mode on command). You can congure PFC parameters using a DCB
map or the pfc priority command in Interface conguration mode. For more information, see Conguring 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 congurations that are received in TLVs from peer devices. By
applying a DCB map with PFC enabled, you enable PFC operations on ingress port trac. To achieve complete lossless handling of trac,
congure PFC priorities on all DCB egress ports.
Data Center Bridging (DCB)
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