Users Guide

The packets come in with packet-dot1p 2 alone use Q2 (as per dot1p to Queue classication – Table 2) on the egress port.
• When Peer sends a PFC message for Priority 2, based on above PRIO2COS table (TABLE 2), Queue 2 is halted.
• Queue 2 starts buering the packets with Dot1p 2. This causes PG6 buer counter to increase on the ingress, since P-dot1p 2 is
mapped to PG6.
• As the PG6 watermark threshold is reached, PFC generats for dot1p 2.
SNMP Support for PFC and Buer Statistics Tracking
Buer Statistics Tracking (BST) feature provides a mechanism to aid in Resource Monitoring and Tuning of Buer Allocation. The Max Use
Count mode provides the maximum value of the counters accumulated over a period of time.
Priority Flow Control (PFC) provides a link level ow control mechanism, which is controlled independently for each frame priority. The goal
of 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:
• dellNetFpEgrQBuSnapshotTable
• dellNetFpIngPgBuSnapshotTable
• dellNetFpStatsPerPgTable
• dellNetPfcPerPrioTable
dellNetFpEgrQBuS
napshotTable
This table fetches the BST statistics at Egress Port for the buer used. This table displays the Snapshot of the
Buer cells used by Unicast and Multicast Data and Control Queues.
dellNetFpIngPgBuS
napshotTable
This table fetches the BST statistics at the Ingress Port for the Shared Cells, and the Headroom cells used per
Priority Group. The snapshot of the Ingress Shared cells used and the Ingress Headroom cells used per Priority
Group, when PFC is enabled, display in this table. This table lists the stack-unit index, port number and the priority
group number.
dellNetFpStatsPerP
gTable
This table fetches the Allocated Min cells, Shared cells, and Headroom cells per Priority Group, the mode in which
the buer cells are allocated — Static or Dynamic and the Used Min Cells, Shared cells and Headroom cells per
Priority Group. The table fetches a value of 0 if the mode of allocation is Static and a value of 1 if the mode of
allocation is Dynamic. This table lists thestack-unit number, port number and priority group number.
dellNetPfcPerPrioTa
ble
This table fetches the number of PFC frames transmitted (PFC Requests) and the number 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
Bits
Priority based Flow Control (PFC) is currently supported on Dell Networking OS for tagged packets based on the packet Dot1p. In certain
data center deployments, VLAN conguration is avoided on the servers and all packets from the servers are untagged. These packets will
carry IP header and can be dierentiated based on the DSCP elds they carry on the server facing switch ports. Requirement is to classify
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 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 classication. This document
will discuss the congurations 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 specic 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 specic Dot1p and PFC is enabled for that Dot1p, switch will transit out PFC frames for that
Dot1p. The packet Dot1p to Queue mapping for classication 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 Networking OS ensures that these mappings are identical. This section discusses the Dell
Networking OS congurations needed for above PFC generation and honoring mechanism to work for the untagged packets.
Data Center Bridging (DCB)
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