Dell S4048-ON, Configuration Manual

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Important Points to Remember
• If you remove a dot1p priority-to-priority group mapping from a DCB map (
no priority pgid
command), the PFC and ETS
parameters revert to their default values on the interfaces on which the DCB map is applied. By default, PFC is not applied on
specific 802.1p priorities; ETS assigns equal bandwidth to each 802.1p priority.
As a result, PFC and lossless port queues are disabled on 802.1p priorities, and all priorities are mapped to the same priority queue
and equally share the port bandwidth.
• To change the ETS bandwidth allocation configured for a priority group in a DCB map, do not modify the existing DCB map
configuration. Instead, first create a new DCB map with the desired PFC and ETS settings, and apply the new map to the
interfaces to override the previous DCB map settings. Then, delete the original dot1p priority-priority group mapping.
If you delete the dot1p priority-priority group mapping (
no priority pgid
command) before you apply the new DCB map,
the default PFC and ETS parameters are applied on the interfaces. This change may create a DCB mismatch with peer DCB
devices and interrupt network operation.
Data Center Bridging: Default Configuration
Before you configure PFC and ETS on a switch see the priority group setting taken into account the following default settings:
DCB is enabled.
PFC and ETS are globally enabled by default.
The default dot1p priority-queue assignments are applied as follows:
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)#
NOTE: In Dell Networking OS we support 4 data queues in MXL.
PFC is not applied on specific dot1p priorities.
ETS: Equal bandwidth is assigned to each port queue and each dot1p priority in a priority group.
To configure PFC and ETS parameters on an S6000 interface, you must specify the PFC mode, the ETS bandwidth allocation for a
priority group, and the 802.1p priority-to-priority group mapping in a DCB map. No default PFC and ETS settings are applied to
Ethernet interfaces.
Configuring Priority-Based Flow Control
Priority-Based Flow Control (PFC) provides a flow control mechanism based on the 802.1p priorities in converged Ethernet traffic
received on an interface and is enabled by default when you enable DCB.
As an enhancement to the existing Ethernet pause mechanism, PFC stops traffic transmission for specified priorities (Class of
Service (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 is to be
stopped. Data Center Bridging Exchange protocol (DCBx) provides the link-level exchange of PFC parameters between peer
devices. PFC allows network administrators to create zero-loss links for Storage Area Network (SAN) traffic that requires no-drop
service, while retaining packet-drop congestion management for Local Area Network (LAN) traffic.
To configure PFC, follow these steps:
1. Create a DCB Map.
CONFIGURATION mode
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Data Center Bridging (DCB)