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Field Description
Total DCBx Frames received Number of DCBx frames received from remote
peer port.
Total DCBx Frame errors Number of DCBx frames with errors received.
Total DCBx Frames unrecognized Number of unrecognizable DCBx frames received.
Generation of PFC for a Priority for Untagged Packets
In order to generate PFC for a particular priority for untagged packets, and configuring PFC for that
priority, you should find the queue number associated with priority from TABLE 1 and Associate a DCB
map to forward the matched DSCP packet to that queue. PFC frames gets generated with PFC priority
associated with the queue when the queue gets congested.
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.
Classification 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).
The internal Priority assigned for the packet by Ingress FP is used by the memory management unit
(MMU) to assign the packet to right queue by indexing the internal-priority to queue map table (TABLE 1)
in hardware.
PRIO2COS setting for honoring the PFC protocol packets from the Peer switches is as per above Packet-
Dot1p->queue table (Table 2).
The packets that come in with packet-dot1p 2 alone will be assigned to PG6 on ingress.
The packets that come in with packet-dot1p 2 alone will use Q1 (as per dot1p to Queue classification –
Table 2) on the egress port.
• When Peer sends a PFC message for Priority 2, based on above PRIO2COS table (TABLE 2), Queue 1 is
halted.
• Queue 1 starts buffering the packets with Dot1p 2. This causes PG6 buffer counter to increase on the
ingress, since P-dot1p 2 is mapped to PG6.
• As the PG6 watermark threshold is reached, PFC will be generated for dot1p 2.
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
Data Center Bridging (DCB)
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