pfcPerPrioTable This table fetches the number of PFC frames transmitted (PFC Requests) and thenumber of PFC frames received (PFC Indications) per priority on a per port basis.This table lists the stack-unit index, port number and priority.Performing PFC Using DSCP Bits Instead of 802.1p BitsPriority based Flow Control (PFC) is currently supported on Dell Networking OS for tagged packets basedon the packet Dot1p. In certain data center deployments, VLAN configuration is avoided on the serversand all packets from the servers are untagged. These packets will carry IP header and can bedifferentiated based on the DSCP fields they carry on the server facing switch ports. Requirement is toclassify these untagged packets from the server based on their DSCP and provide PFC treatment.Dell Networking OS Releases 9.3(0.0) and earlier provide CLI support to specify the priorities for whichPFC is enabled on each port. This feature is applicable only for the tagged packets based on the incomingpacket Dot1p and Dot1p based queue classification. This document will discuss the configurationsrequired 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 aspecific priority is received from the peer switch, the queue corresponding to that Dot1p is halted fromscheduling on that port, thus honoring the PFC from the peer. If a queue is congested due to packetswith 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 ofDot1p to the Queue to be halted on the egress used for PFC honoring. Dell Networking OS ensures thatthese mappings are identical. This section discusses the Dell Networking OS configurations needed forabove 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 mappedto PG7. A priority for which PFC has to be generated is assigned to a PG other than PG7 (say PG6) andbuffer 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 thathas ingress this port PG but still queued up in egress pipeline. However, there is no direct mappingbetween 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 MappingInternal-priority0 1 2 3 4 5 6 7Queue 2 0 1 3 4 5 6 7Default dot1p to queue configuration is as follows:Table 19. Dot1p to Queue MappingPacket-Dot1p0 1 2 3 4 5 6 7Queue 2 0 1 3 4 5 6 7254 Data Center Bridging (DCB)
