Concept Guide

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 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 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 EMC Networking OS ensures that these mappings are identical. This section discusses
the Dell EMC Networking OS congurations 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 buer watermark is set on PG6 so as to generate PFC.
In ingress, the buers 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 modied and enhanced as follows for the device:
Table 21. Priority to Queue Mapping
Internal-
priority
0 1 2 3 4 5 6 7
Queue
2 0 1 3 4 5 6 7
Default dot1p to queue conguration is as follows:
Table 22. Dot1p to Queue Mapping
Packet-
Dot1p
0 1 2 3 4 5 6 7
Queue
2 0 1 3 4 5 6 7
PFC and ETS Conguration Examples
This section contains examples of how to congure and apply DCB policies on an interface.
Using PFC to Manage Converged Ethernet Trac
To use PFC for managing converged Ethernet trac, use the following command:
dcb-map stack-unit all dcb-map-name
Operations on Untagged Packets
The below is example for enabling PFC for priority 2 for tagged packets. Priority (Packet Dot1p) 2 will be mapped to PG6 on PRIO2PG
setting. All other Priorities for which PFC is not enabled are mapped to default PG – PG7.
Classication rules on ingress (Ingress FP CAM region) matches incoming packet-dot1p and assigns an internal priority (to select queue as
per Table 1 and Table 2).
Data Center Bridging (DCB)
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