SNMP Support for PFC and Buffer Statistics TrackingBuffer Statistics Tracking (BST) feature provides a mechanism to aid in Resource Monitoring and Tuning of Buffer Allocation. The Max UseCount mode provides the maximum value of the counters accumulated over a period of time.Priority Flow Control (PFC) provides a link level flow control mechanism, which is controlled independently for each frame priority. The goalof this mechanism is to ensure zero loss under congestion in DCB networks.Dell Networking OS provides SNMP support for monitoring PFC and BST counters, and statistics. The enhancement is made on DELL-NETWORKING-FPSTATS-MIB with additional tables to display the PFC and BST counters and statistics.The following tables are available in DELL-NETWORKING-FPSTATS-MIB:• dellNetFpEgrQBuffSnapshotTable• dellNetFpIngPgBuffSnapshotTable• dellNetFpStatsPerPgTable• dellNetPfcPerPrioTabledellNetFpEgrQBuffSnapshotTableThis table fetches the BST statistics at Egress Port for the buffer used. This table displays the Snapshot of theBuffer cells used by Unicast and Multicast Data and Control Queues.dellNetFpIngPgBuffSnapshotTableThis table fetches the BST statistics at the Ingress Port for the Shared Cells, and the Headroom cells used perPriority Group. The snapshot of the Ingress Shared cells used and the Ingress Headroom cells used per PriorityGroup, when PFC is enabled, display in this table. This table lists the stack-unit index, port number and the prioritygroup number.dellNetFpStatsPerPgTableThis table fetches the Allocated Min cells, Shared cells, and Headroom cells per Priority Group, the mode in whichthe buffer cells are allocated — Static or Dynamic and the Used Min Cells, Shared cells and Headroom cells perPriority Group. The table fetches a value of 0 if the mode of allocation is Static and a value of 1 if the mode ofallocation is Dynamic. This table lists thestack-unit number, port number and priority group number.dellNetPfcPerPrioTableThis table fetches the number of PFC frames transmitted (PFC Requests) and the number of PFC framesreceived (PFC Indications) per priority on a per port basis. This table lists the stack-unit index, port number andpriority.Performing PFC Using DSCP Bits Instead of 802.1pBitsPriority based Flow Control (PFC) is currently supported on Dell Networking OS for tagged packets based on the packet Dot1p. In certaindata center deployments, VLAN configuration is avoided on the servers and all packets from the servers are untagged. These packets willcarry IP header and can be differentiated based on the DSCP fields they carry on the server facing switch ports. Requirement is to classifythese 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 which PFC is enabled on each port. Thisfeature is applicable only for the tagged packets based on the incoming packet Dot1p and Dot1p based queue classification. This documentwill 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 fromthe peer switch, the queue corresponding to that Dot1p is halted from scheduling on that port, thus honoring the PFC from the peer. If aqueue is congested due to packets with a specific Dot1p and PFC is enabled for that Dot1p, switch will transit out PFC frames for thatDot1p. The packet Dot1p to Queue mapping for classification on the ingress must be same as the mapping of Dot1p to the Queue to behalted on the egress used for PFC honoring. Dell Networking OS ensures that these mappings are identical. This section discusses the DellNetworking 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 PFChas 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.Data Center Bridging (DCB) 261
