A site has two internet circuits: Circuit A with 500 Mbps capacity and Circuit B with 100 Mbps capacity. Which path policy configuration will ensure traffic is automatically shifted from a saturated circuit to the circuit with available bandwidth?

To automatically shift traffic from a saturated circuit to one with available bandwidth, both circuits must be configured as active paths. This active-active configuration allows the Palo Alto Networks SD-WAN solution to monitor the utilization of both links simultaneously. When one circuit's bandwidth usage exceeds its configured saturation threshold, the system identifies it as saturated and dynamically steers new application sessions to the other active circuit that has available capacity. This ensures optimal performance and efficient use of all available bandwidth, which is the core requirement of the question.

A. Circuit A as an active, Circuit B as a backup: An active/backup policy only fails over upon significant link degradation (high loss/latency/jitter) or complete failure, not saturation.
B. Circuit B as an active, Circuit A as a backup: This is also an active/backup configuration and does not shift traffic based on link saturation.
D. Circuit B as an L3 failure path: An L3 failure path is a specific failover mechanism used when the primary path's next-hop gateway becomes unreachable, not for managing link saturation.

1. Palo Alto Networks Prisma SD-WAN Administrator’s Guide: In the section "Define Application Path and Security Policy Rules," the guide details path types. It defines an Active path as one that is "used for traffic if it is in a healthy state. You can have multiple active paths." In contrast, a Backup path is "used for traffic only if all Active paths are in an unusable state." This distinction confirms that only an active-active setup (Option C) allows for simultaneous use and dynamic load shifting.

2. Palo Alto Networks Prisma SD-WAN Administrator’s Guide: The section "Link Quality and Application Metrics" explains how the system monitors path performance. It states, "When a link is saturated, new sessions are assigned to other links that are not saturated." This functionality is inherent to policies where multiple active paths are configured, allowing the system to make intelligent, real-time path selection decisions based on utilization.