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Priority-Group Conguration Notes
When you congure 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 3. Each priority group can support more
than one data queue.
• If you congure more than one priority group as strict priority, the higher numbered priority queue is given preference when scheduling
data trac.
Conguring Priority-Based Flow Control
Priority-Based Flow Control (PFC) provides a ow control mechanism based on the 802.1p priorities in converged Ethernet trac received
on an interface and is enabled by default when you enable DCB.
As an enhancement to the existing Ethernet pause mechanism, PFC stops trac transmission for specied priorities (Class of Service
(CoS) values) without impacting other priority classes. Dierent trac types are assigned to dierent priority classes.
When trac congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of the trac 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) trac that requires no-drop service, while retaining
packet-drop congestion management for Local Area Network (LAN) trac.
To congure 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 ow 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.
Data Center Bridging (DCB)
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