Configuring Priority-Based Flow Control - Dell S4820T Configuration Manual

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 PFC group.
CONFIGURATION mode
priority-group group-num {bandwidth bandwidth | strict-priority} pfc on
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.
Data Center Bridging (DCB)
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