User Manual

Rev 4.60
Mellanox Technologies
35
3.9 Differentiated Services Code Point (DSCP)
DSCP is a mechanism used for classifying network traffic on IP networks. It uses the 6-bit Dif-
ferentiated Services Field (DS or DSCP field) in the IP header for packet classification purposes.
Using Layer 3 classification enables you to maintain the same classification semantics beyond
local network, across routers.
Every transmitted packet holds the information allowing network devices to map the packet to
the appropriate 802.1Qbb CoS. For DSCP based PFC the packet is marked with a DSCP value in
the Differentiated Services (DS) field of the IP header.
3.9.1 Setting the DSCP in the IP Header
Marking DSCP value in the IP header is done differently for IP packets constructed by the NIC
(e.g. RDMA traffic) and for packets constructed by the IP stack (e.g. TCP traffic).
• For IP packets generated by the IP stack, the DSCP value is provided by the IP stack.
The NIC does not validate the match between DSCP and Class of Service (CoS) values.
CoS and DSCP values are expected to be set through standard tools, such as PowerShell
command New-NetQosPolicy using PriorityValue8021Action and DSCPAction flags
respectively.
• For IP packets generated by the NIC (RDMA), the DSCP value is generated according
to the CoS value programmed for the interface. CoS value is set through standard tools,
such as PowerShell command New-NetQosPolicy using PriorityValue8021Action flag.
The NIC uses a mapping table between the CoS value and the DSCP value configured
through the RroceDscpMarkPriorityFlow- Control[0-7] Registry keys
3.9.2 Configuring Quality of Service for TCP and RDMA Traffic
Step 1. Verify that DCB is installed and enabled (is not installed by default).
Step 2. Import the PowerShell modules that are required to configure DCB.
Step 3. Configure DCB.
Step 4. Enable Network Adapter QoS.
Step 5. Enable Priority Flow Control (PFC) on the specific priority 3,5.
3.9.3 Configuring DSCP for TCP Traffic
• Create a QoS policy to tag All TCP/UDP traffic with CoS value 1 and DSCP value 9.
DSCP can also be configured per protocol.
$ Install-WindowsFeature Data-Center-Bridging
$ import-module NetQos
$ import-module DcbQos
$ import-module NetAdapter
$ Set-NetQosDcbxSetting -Willing 0
$ Set-NetAdapterQos -Name "Cx3Pro_ETH_P1" -Enabled 1
$ Enable-NetQosFlowControl 3,5
$ New-NetQosPolicy "DEFAULT" -PriorityValue8021Action 3 -DSCPAction 9
$ New-NetQosPolicy "TCP" -IPProtocolMatchCondition TCP -PriorityValue8021Action 3 -DSCPAction 16
$ New-NetQosPolicy "UDP" -IPProtocolMatchCondition UDP -PriorityValue8021Action 3 -DSCPAction 32