Users Guide

7–RoCE Configuration
Configuring DCQCN
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Configuring DCQCN
Data Center Quantized Congestion Notification (DCQCN) is a feature that
determines how an RoCE receiver notifies a transmitter that a switch between
them has provided an explicit congestion notification (notification point), and how
a transmitter reacts to such notification (reaction point).
This section provides the following information about DCQCN configuration:
 DCQCN Terminology
 DCQCN Overview
 DCB-related Parameters
 Global Settings on RDMA Traffic
 Configuring DSCP-PFC
 Enabling DCQCN
 Configuring CNP
 DCQCN Algorithm Parameters
 MAC Statistics
 Script Example
 Limitations
DCQCN Terminology
The following terms describe DCQCN configuration:
 ToS (type of service) is a single-byte in the IPv4 header field. ToS comprises
two ECN least significant bits (LSB) and six Differentiated Services Code
Point (DSCP) most significant bits (MSB). For IPv6, traffic class is the
equivalent of the IPv4 ToS.
 ECN (explicit congestion notification) is a mechanism where a switch adds
to outgoing traffic an indication that congestion is imminent.
 CNP (congestion notification packet) is a packet used by the notification
point to indicate that the ECN arrived from the switch back to the reaction
point. CNP is defined in the Supplement to InfiniBand Architecture
Specification Volume 1 Release 1.2.1, located here:
https://cw.infinibandta.org/document/dl/7781
 VLAN Priority is a field in the L2 vLAN header. The field is the three MSBs
in the vLAN tag.
 PFC (priority-based flow control) is a flow control mechanism that applies to
traffic carrying a specific vLAN priority.