SLA Profiles and SD-WAN Policies Overview
Contrail Service Orchestration (CSO) enables you to create service-level agreement (SLA) profiles and map them to software-defined WAN (SD-WAN) policies for traffic management.
SLA profiles are created for applications or groups of applications for all tenants. An SLA profile consists of a set of configurable constraints that can be defined in the unified portal for both the Administration and Customer Portals. Table 1 lists the categories of configurable constraints that are defined in an SLA profile.
Table 1: SLA Profile Categories
SLA profile parameters
You can define one or more than one of the following SLA profile parameters:
Path preference and failover
Paths are the WAN links to be used for the SLA profile. You can select MPLS, Internet, or any link as the preferred path. MPLS is more latency-sensitive than Internet.
You can trigger the path failover criteria when any of the SLA parameters is violated.or when all the SLA parameters are violated.
Class of service
Class of service (CoS) provides different levels of service assurances to various forms of traffic. CoS enables you to divide traffic into classes and offer an assured service level for each class. The classes of service listed in increasing order of priority and sensitivity to latency are best effort, voice, interactive video, streaming audio or video, control, and business essential. The default CoS is voice.
Rate limiters are defined for traffic shaping and efficient bandwidth utilization. You can define the following rate limiters:
You must define at least one of the SLA parameters or path preference. You cannot leave both path preference and SLA parameters fields blank at the same time.
Applications are classified into the following categories:
Cacheable applications, which refer to applications or application groups that are stored in the application cache when they are recognized by the device. After they are stored in the application cache, subsequent sessions are routed directly through the correct WAN link.
Non-cacheable applications, which refer to applications or application groups that are not stored in the application cache and all sessions are first routed through the default path, and then routed to the correct WAN link based on the SD-WAN policy.
Policy intents consist of the following parameters:
Source—A source endpoint that you can choose from a list of sites, site groups, and departments or a combination of all of these. The SD-WAN policy intent is applied to the selected source endpoint.
Destination—A destination endpoint that you can choose from a list of applications and predefined or custom application groups. You can select a maximum of 32 applications or application groups as destination endpoints. The SD-WAN policy intent is applied to the selected destination endpoint.
Traffic Steering Profile—Depending on whether you want to apply the policy intent to site-to-site traffic or breakout traffic, you can associate the traffic steering profile with the policy intent. The following options are available:
SLA-based steering profile— Applicable for site-to-site traffic
Path-based steering profile— Applicable for site-to-site traffic
Breakout profile—Applicable for breakout traffic (local, central, or cloud).
Intent name—A unique name for the SD-WAN policy intent.
SD-WAN supports advanced policy-based routing (APBR). APBR enables you to dynamically define the routing behavior of the SD-WAN network based on applications. Dynamic application-based routing makes it possible to define policies and to switch WAN links on the fly based on the application's defined SLA parameters. The APBR mechanism classifies sessions based on applications and application signatures and uses policy intents to identify the best possible route for the application. When the best possible route does not meet the application's defined SLA requirements, the SD-WAN network finds the next best possible route to meet SLA requirements.
For example, consider an application in a site. If you want the application group to use custom throughput, latency, or jitter, you can create an SLA profile with these custom values. You can then create an intent and configure the intent with the application and apply the custom SLA profile. When the intent is deployed, CSO determines the best suited WAN link to route traffic based in the application. If the WAN link fails to meet SLA requirements in runtime, the SD-WAN network switches WAN links to the next best suited path.
On the basis of the configured traffic-based steering profile constraints, you can categorize SD-WAN policies into three types:
Path-based steering policy—If only the path preference is defined and none of the SLA parameters are defined in the SLA profile, then the policy is called a path-based steering policy. In path-based steering profile, you can define the path (MPLS or Internet) that must be used for a given traffic type profile, You cannot configure SLA parameters or path failover criteria for a path-based steering profile. The traffic type profile must be in enabled state in order to be used in any profile.
SLA-based steering policy—If one or more SLA parameters in the SLA profile are defined, then the policy is called an SLA-based steering policy. In an SLA-based steering profile, each profile is associated with a traffic type profile and tracks the SLA parameters such as packet loss, Jitter and RTT. The traffic type profile must be in enabled state in order to be used in any profile. Based on your requirements, you can choose the recommended SLA threshold or enter custom SLA threshold for the traffic type profile. You can even set the path preference (Any, MPLS, or Internet) to switch traffic from one WAN interface to another based on the path failover criteria.
When an intent is deployed on a site, if the WAN link chosen by the SD-WAN network does not meet the SLA requirements and the network performance deteriorates, then the site switches WAN links to meet the SLA requirements. The link switching is recorded as an SD-WAN event and displayed in the SD-WAN Events page in the customer portal and the Tenant_name SLA Performance pages in the administration and customer portals.
Breakout policy—If local breakout, central breakout, or cloud breakout parameters are defined, then the policy is called a breakout policy.