Quality of Service in Contrail

Overview: Quality of Service

Quality of service (QoS) in networking provides the ability to control reliability, bandwidth, latency, and other traffic management features. Network traffic can be marked with QoS bits (DSCP, 802.1p, and MPLS EXP) that intermediate network switches and routers can use to provide service guarantees.

Contrail QoS Model

The QoS model in Contrail Networking has the following features:

• All packet forwarding devices, such as vRouter and the gateway, combine to form a system.

• Interfaces to the system are the ports from which the system sends and receives packets, such as tap interfaces and physical ports.

• Fabric interfaces are where the overlay traffic is tunneled.

• QoS is applied at the ingress to the system, for example, upon traffic from the interfaces to the fabric.

• At egress, packets are stripped of their tunnel headers and sent to interface queues, based on the forwarding class. No marking from the outer packet to the inner packet is considered at this time.

Features of Fabric Interfaces

Fabric interfaces, unlike other interfaces, are always shared. Therefore, fabric interfaces are common property. Consequently, traffic classes and QoS marking on the fabric must be controlled by the system administrator. The administrator might choose to provision different classes of service on the fabric.

In Contrail, classes of service are determined by both of the following:

• Queueing on the fabric interface, including queues, scheduling of queues, and drop policies, and

• forwarding class, a method of marking that controls how packets are sent to the fabric, including marking and identifying which queue to use.

Tenants can define which forwarding class their traffic can use, deciding which packets use which forwarding class. The Contrail QoS configuration object has a mapping table, mapping the incoming DSCP or 802.1p value to the forwarding class mapping.

The QoS configuration can also be applied to a virtual network, an interface, or a network policy.

QoS Configuration Parameters for Provisioning

Configuring QoS in Contrail Networking Release 5.0 and Later

This section describes how to provision QoS in Contrail Networking release 5.0 and later.

1. Define the hardware queues and priority group in the instances.yaml file under the vrouter role as shown below.

2. In the already provisioned setup, define the QoS configuration in the /etc/contrail/common_vrouter.env file as shown in the following sample.

3. Execute the execute docker-compose up -d under /etc/contrail/vrouter/ command.

Queuing Implementation

The vRouter provides the infrastructure to use queues supplied by the network interface, a method that is also called hardware queueing. Network interface cards (NICs) that implement hardware queueing have their own set of scheduling algorithms associated with the queues. The Contrail implementation is designed to work with most NICs, however, the method is tested only on an Intel-based 10G NIC, also called Niantic.

Contrail QoS Configuration Objects

Contrail QoS configuration objects include the:

• forwarding class

• QoS configuration object (qos-config)

The forwarding class object specifies parameters for marking and queuing, including:

• The DSCP, 802.1p, and MPLS EXP values to be written on packets.

• The queue index to be used for the packet.

The QoS configuration object specifies a mapping from DSCP, 802.1p, and MPLS EXP values to the corresponding forwarding class.

The QoS configuration has an option to specify the default forwarding class ID to use to select the forwarding class for all unspecified DSCP, 802.1p, and MPLS EXP values.

If the default forwarding class ID is not specified by the user, it defaults to the forwarding class with ID 0.

Processing of QoS marked packets to look up the corresponding forwarding class to be applied works as follows:

• For an IP packet, the DSCP map is used .

• For a Layer 2 packet, the 802.1p map is used.

• For an MPLS-tunneled packet with MPLS EXP values specified, the EXP bit value is used with the MPLS EXP map.

• If the QoS configuration is untrusted, only the default forwarding class is specified, and all incoming values of the DSCP, 802.1p, and EXP bits in the packet are mapped to the same default forwarding class.

Figure 1 shows the processing of QoS packets.

Figure 1: Processing of QoS Packets

A virtual machine interface, virtual network, and network policy can refer to the QoS configuration object. The QoS configuration object can be specified on the vhost so that underlay traffic can also be subjected to marking and queuing. See Figure 2.

Figure 2: Referring to the QoS Object

Example: Mapping Traffic to Forwarding Classes

This example shows how traffic forwarding classes are defined and how the QoS configuration object is defined to map the QoS bits to forwarding classes.

Table 1 shows two forwarding class objects defined. FC1 marks the traffic with high priority values and queues it to Queue 0. FC2 marks the traffic as best effort and queues the traffic to Queue 1.

In Table 2, the QoS configuration object DSCP values of 10, 18, and 26 are mapped to a forwarding class with ID 1, which is forwarding class FC1. All other IP packets are mapped to the forwarding class with ID 2, which is FC2. All traffic with an 802.1p value of 6 or 7 are mapped to forwarding class FC1, and the remaining traffic is mapped to FC2.

QoS Configuration Object Marking on the Packet

The following sections describes how QoS configuration object marking is handled in various circumstances.

• Traffic Originated by a Virtual Machine Interface
• Traffic Destined to a Virtual Machine Interface
• Traffic from a vhost Interface
• Traffic from fabric interface
• QoS Configuration Priority by Level

Queuing

Contrail Networking supports QoS. These sections provide an overview of the queuing features available in Contrail Networking.

The queue to which a packet is sent is specified by the forwarding class.

• Queue Selection in Datapath
• Hardware Queueing in Linux kernel based vRouter
• Parameters for QoS Scheduling Configuration