Users Guide

dellNetFpStatsPerP
gTable
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 the
stack-unit number, port number and priority group number.
dellNetPfcPerPrioT
able
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 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 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 Networking OS ensures that these mappings
are identical. This section discusses the Dell 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:
Data Center Bridging (DCB) 273