When specifically configuring a load balancing policy, you need to first make sure the Load Balancing option is set to Enabled in the Global Preferences section of the SD-WAN & Traffic Shaping page, as previously shown in Figure 6-5. If you also set the Preferred Uplink option to Load Balance, the option to choose an uplink performance class is also shown.
In the example shown in Figure 6-7, the device will monitor all available transport paths and load balance matching traffic flows across paths matching the performance requirements of the selected performance class—in this case, a custom performance class called O365. This helps to ensure that all available bandwidth is provided to the application while also ensuring that all the participating transport networks are compliant with your custom performance criteria.
Figure 6-7 Custom “Office 365” Uplink Policy
Load balancing policies also take into consideration the configured available bandwidth for all matching uplinks, which is used to perform weighted load balancing on a per-flow basis to help maintain equal relative utilization along each path. As an example, if the difference between the configured available bandwidth of the primary and secondary WAN uplinks is a 1:4 ratio, then the MX would load balance matching flows between those uplinks in a matching 1:4 ratio.
Pro Tip
This load balancing behavior also applies to traffic that is load balanced via the Global Preferences configuration.
Basic Policy-Based Routing
Figure 6-8 is an example of configuring a non-business-critical application, Facebook, with a preferred uplink of WAN 2 and setting it to fail over only if that uplink is completely unavailable. In this configuration, Facebook traffic will continue to use WAN 2 irrespective of the performance score for that uplink as long as the uplink is available, since performance-based checks are not configured.
Figure 6-8 Uplink Selection Policy to Route All Facebook Traffic over WAN 2 Unless Unavailable