Dynamic path selection (DPS) policies in the Dashboard can be configured as a simple mapping of an application to a specific uplink or configured with multiple conditional policies to ensure critical application traffic always takes the best available path. Even though the configuration is directed to an uplink interface, there are multiple virtual paths that may be taken through that interface. The exact virtual transport path chosen for the traffic will be dependent on the overall Auto VPN architecture (e.g., number of hubs).
Two of the primary configurations that influence these uplink decisions are the primary uplink preference and load balancing configuration, located in the Global Preferences section of the Security & SD-WAN > SD-WAN & Traffic Shaping page, as shown in Figure 6-5.
Pro Tip
It’s important to note that if the Load Balancing option is set to Disabled in the Global Preferences section, none of the configured load balancing policies will take effect.
Figure 6-5 Global Preferences Section of the SD-WAN & Traffic Shaping Page
Next you’ll explore a few policy configuration examples for uplink selection based on commonly seen use cases. In the following examples, assume that the WAN1 uplink is a high-speed fiber network that you want to handle all your sensitive application traffic, and that the WAN2 uplink is a legacy DSL connection that you prefer to use as a backup connection or for noncritical application traffic.
Global Preference Policy
This section defines a basic example policy to act as a fallback policy. This policy will act as a catch-all, policy-based routing decision for traffic whose priority is somewhere between that of a business-critical application and an explicitly noncritical application—in this example, the traffic is labeled the “All Social web & photo sharing” category.
As a result, the policy shown in Figure 6-6 is configured to use the uplink preferences defined in the Global Preferences section of the SD-WAN & Traffic Shaping page (see Figure 6-5) with no other explicit requirements. In this case, because the Load Balancing option is set to Enabled in the Global Preferences section, you would see application traffic matching this policy load balanced across both uplinks.
Pro Tip
A policy such as this is not strictly necessary with most designs, as any traffic not matching an existing policy will by default follow the global routing preferences for primary uplink selection, load balancing, and failover.
Figure 6-6 Uplink Selection Policy to Send All Social Web & Photo Sharing Traffic Out Uplinks Based on the Global Routing Preference, Configured to Load Balance