Dell S4820T, Configuration Manual

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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 configured.
NOTE: Dell Networking OS Behavior : By default, no lossless queues are configured on a port.
A limit of two lossless queues is supported on a port. If the amount of priority traffic that you configure to
be paused exceeds the two lossless queues, an error message displays.
Configuring PFC in a DCB Map
An S4820T switch supports the use of a DCB map in which you configure priority-based flow control
(PFC) setting. To configure PFC parameters, you must apply a DCB map on an S4820T interface. This
functionality is supported on the S4820T platform.
PFC Configuration Notes
PFC provides flow control based on the 802.1p priorities in a converged Ethernet traffic 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 traffic transmission for specified priorities (CoS values) without
impacting other priority classes. Different traffic types are assigned to different priority classes.
When traffic congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of
the traffic 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 traffic that requires no-
drop service, while at the same time retaining packet-drop congestion management for LAN traffic.
On switch, PFC is enabled by default on Ethernet ports (
pfc mode on
command). You can configure
PFC parameters using a DCB map or the
pfc priority
command in Interface configuration mode. For
more information, see Configuring 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
configurations that are received in TLVs from peer devices. By applying a DCB map with PFC enabled,
you enable PFC operations on ingress port traffic. To achieve complete lossless handling of traffic,
configure 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 configured. When a DCB input policy with PFC profile is
configured or unconfigured on an interface or a range of interfaces not receiving any traffic, interfaces
with PFC settings that receive appropriate PFC-enabled traffic (unicast, mixed-frame-size traffic) display
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Data Center Bridging (DCB)