Users Guide

NOTE: Although, each port on the S4810, S4820T, and S5000 devices support 8 QoS queues, you can congure only 4
QoS queues (0-3) to manage data trac. The remaining 4 queues (4-7) are reserved for control trac.
Dell(conf)#do show qos dot1p-queue-mapping
Dot1p Priority : 0 1 2 3 4 5 6 7
Queue : 0 0 0 1 2 3 3 3
Dell(conf)#
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 S4820T 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 S4820T interface. This functionality is supported on the S4820T 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.
Data Center Bridging (DCB)
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