Administrator Guide

Dell EMC Networking OS Releases 9.3(0.0) and earlier provide CLI support to specify the priorities for which PFC is enabled on each port.
This feature is applicable only for the tagged packets based on the incoming packet Dot1p and Dot1p based queue classification. This
document will discuss the configurations required to support PFC for untagged packets based on incoming packet DSCP.
For the tagged packets, Queue is selected based on the incoming Packet Dot1p. When PFC frames for a specific priority is received from
the peer switch, the queue corresponding to that Dot1p is halted from scheduling on that port, thus honoring the PFC from the peer. If a
queue is congested due to packets with a specific Dot1p and PFC is enabled for that Dot1p, switch will transit out PFC frames for that
Dot1p. The packet Dot1p to Queue mapping for classification on the ingress must be same as the mapping of Dot1p to the Queue to be
halted on the egress used for PFC honoring. Dell EMC Networking OS ensures that these mappings are identical. This section discusses
the Dell EMC Networking OS configurations needed for above PFC generation and honoring mechanism to work for the untagged
packets.
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 24. Priority to Queue Mapping
Internal-priority Queue
0 2
1 0
2 1
3 3
4 4
5 5
6 6
7 7
Default dot1p to queue configuration is as follows:
Table 25. Dot1p to Queue Mapping
Packet-Dot1p Queue
0 2
1 0
2 1
3 3
4 4
5 5
6 6
7 7
252 Data Center Bridging (DCB)