Administrator Guide

● If you configure more than one priority group as strict priority, the higher numbered priority queue is given preference when
scheduling data traffic.
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
dcb-map dcb-map-name
The dcb-map-name variable can have a maximum of 32 characters.
2. Create a priority group.
CONFIGURATION mode
priority-group group-num {bandwidth bandwidth | strict-priority} [[committed | peak]
bandwidth [burst-size] [peak | committed] bandwidth [burst-size]] pfc {on | off}
The range for priority group is from 0 to 7.
Set the bandwidth in percentage. The percentage range is from 1 to 100% in units of 1%.
Committed and peak bandwidth is in megabits per second. The range is from 0 to 40000.
Committed and peak burst size is in kilobytes. Default is 50. The range is from 0 to 10000.
The pfc on command enables priority-based flow control.
3. Specify the dot1p priority-to-priority group mapping for each priority.
priority-pgid dot1p0_group_num dot1p1_group_num ...dot1p7_group_num
Priority group range is from 0 to 7. All priorities that map to the same queue must be in the same priority group.
Leave a space between each priority group number. For example: priority-pgid 0 0 0 1 2 4 4 4 in which priority group 0 maps
to dot1p priorities 0, 1, and 2; priority group 1 maps to dot1p priority 3; priority group 2 maps to dot1p priority 4; priority group
4 maps to dot1p priorities 5, 6, and 7.
Dell Networking OS Behavior: As soon as you apply a DCB policy with PFC enabled on an interface, DCBx starts exchanging
information with PFC-enabled peers. The IEEE802.1Qbb, CEE, and CIN versions of PFC Type, Length, Value (TLV) are
supported. DCBx also validates PFC configurations that are received in TLVs from peer devices.
NOTE: You cannot enable PFC and link-level flow control at the same time on an interface.
Dell Networking OS does not support MACsec Bypass Capability (MBC).
NOTE:
We recommend that you do not use the dcb-policy input, dcb-policy output, dcb-input, dcb-
output, and priority-group commands as those are removed from Release 9.6.(0.0).
Configuring Lossless Queues
DCB also supports the manual configuration of lossless queues on an interface when PFC mode is turned off.
Prerequisite: A DCB with PFC configuration is applied to the interface with the following conditions:
● PFC mode is off (no pfc mode on).
● No PFC priority classes are configured (no pfc priority priority-range).
The configuration of no-drop queues provides flexibility for ports on which PFC is not needed but lossless traffic should egress
from the interface.
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Data Center Bridging (DCB)