Users Guide

The conguration of no-drop queues provides exibility for ports on which PFC is not needed but lossless trac should egress from
the interface.
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 type slot/port
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 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 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.
Conguring PFC in a DCB Map
An S5000 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 S5000 interface. This functionality is supported on the S5000 platform.
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 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.
When you apply or remove a DCB input policy from an interface, one or two CRC errors are expected to be noticed on the ingress
ports for each removal or attachment of the policy. This behavior occurs because the port is brought down when PFC is congured.
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Data Center Bridging (DCB)