Comprehensive and Detailed Explanation

Prisma SD-WAN utilizes Link Quality Monitoring (LQM) to maintain a real-time health score for every WAN path.

To ensure the system knows the quality of a path before sending critical user traffic onto it, the ION device uses Active Probing.

Mechanism:The ION sends synthetic probe packets (typically UDP) across the Secure Fabric (VPN tunnels) and Direct Internet paths to its peers. These probes measure Latency, Jitter, andPacket Loss.

Active vs. Passive:While the systemdoesuse Passive Monitoring (observing actual user flows) when traffic is present to reduce overhead, Active Probes are essential for idle links or backup paths. Without active probing, the ION would have no data to make an intelligent steering decision for thefirstpacket of a new video call. This ensures that "Real-Time" policies always have up-to-date metrics to select the best path immediately.