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When you configure priority groups in a DCB map:
• A priority group consists of 802.1p priority values that are grouped together for similar bandwidth
allocation and scheduling, and that share the same latency and loss requirements. All 802.1p priorities
mapped to the same queue must be in the same priority group.
• In a DCB map, each 802.1p priority must map to a priority group.
• The maximum number of priority groups supported in a DCB map on an interface is equal to the
number of data queues (4) on the port. Each priority group can support more than one data queue.
• You can enable PFC on a maximum of two priority queues on an interface.
• 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 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
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Data Center Bridging (DCB)