Users Guide

PRIORITY to PG mapping (PRIO2PG) is on the ingress for each port. By default, all priorities are mapped to PG7. A priority for which PFC
has to be generated is assigned to a PG other than PG7 (say PG6) and buffer watermark is set on PG6 so as to generate PFC.
In ingress, the buffers are accounted at per PG basis and would indicate the number of the packets that has ingress this port PG but still
queued up in egress pipeline. However, there is no direct mapping between the PG and Queue.
Packet is assigned an internal priority on the ingress pipeline based on the queue to which it is destined. This Internal-priority to Queue
mapping has been modified and enhanced as follows for the device:
Table 18. Priority to Queue Mapping
Internal-
priority
0 1 2 3 4 5 6 7
Queue
2 0 1 3 4 5 6 7
Default dot1p to queue configuration is as follows:
Table 19. Dot1p to Queue Mapping
Packet-
Dot1p
0 1 2 3 4 5 6 7
Queue
2 0 1 3 4 5 6 7
PFC and ETS Configuration Examples
This section contains examples of how to configure and apply DCB policies on an interface.
Using PFC to Manage Converged Ethernet Traffic
To use PFC for managing converged Ethernet traffic, use the following command:
dcb-map stack-unit all dcb-map-name
Operations on Untagged Packets
The below is example for enabling PFC for priority 2 for tagged packets. Priority (Packet Dot1p) 2 will be mapped to PG6 on PRIO2PG
setting. All other Priorities for which PFC is not enabled are mapped to default PG – PG7.
Classification rules on ingress (Ingress FP CAM region) matches incoming packet-dot1p and assigns an internal priority (to select queue as
per Table 1 and Table 2).
The internal Priority assigned for the packet by Ingress FP is used by the memory management unit (MMU) to assign the packet to right
queue by indexing the internal-priority to queue map table (TABLE 1) in hardware.
PRIO2COS setting for honoring the PFC protocol packets from the Peer switches is as per above Packet-Dot1p->queue table (Table 2).
The packets that come in with packet-dot1p 2 alone will be assigned to PG6 on ingress.
The packets that come in with packet-dot1p 2 alone will use Q1 (as per dot1p to Queue classification – Table 2) on the egress port.
• When Peer sends a PFC message for Priority 2, based on above PRIO2COS table (TABLE 2), Queue 1 is halted.
• Queue 1 starts buffering the packets with Dot1p 2. This causes PG6 buffer counter to increase on the ingress, since P-dot1p 2 is
mapped to PG6.
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Data Center Bridging (DCB)