Deployment Guide

dellNetFpIngPgB
uffSnapshotTabl
e
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.
dellNetFpStatsPe
rPgTable
This table fetches the Allocated Min cells, Shared cells, and Headroom cells per Priority Group, the mode
in which the buffer 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.
dellNetPfcPerPri
oTable
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 EMC Networking OS for tagged packets based on the packet
Dot1p. In certain data center deployments, VLAN configuration is avoided on the servers and all packets from the servers are
untagged. These packets will carry IP header and can be differentiated based on the DSCP fields 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 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 20. Priority to Queue Mapping
Internal-priority Queue
0 2
1 0
2 1
3 3
4 4
5 5
6 6
Data Center Bridging (DCB) 247