The Event Logs > System page is the primary location within the Prisma SD-WAN portal for troubleshooting control plane issues, such as VPN tunnel failures. This log captures detailed system-level messages, including the step-by-step Internet Key Exchange (IKE) negotiation process. When a tunnel fails to establish due to a misconfiguration, such as a mismatched pre-shared key or incompatible crypto proposals, specific error codes like "AUTHFAILED" or "NOPROPOSALCHOSEN" are recorded here. This provides the granular detail necessary to diagnose the root cause of the "VPNDOWN" alarm.

A. Flow Browser: This tool is used for inspecting individual data plane traffic flows (sessions) after a tunnel is established, not for diagnosing control plane tunnel negotiation failures.

C. Site Summary > Topology: This provides a high-level visual representation of tunnel status (up or down) but lacks the detailed error logs needed to determine why the tunnel is down.

D. Link Quality Graphs: These graphs display performance metrics like latency, jitter, and loss for the underlying WAN circuits, not the specific error codes from the IKE negotiation process.

1. Palo Alto Networks Prisma SD-WAN Administrator's Guide: In the section "Monitor Events," the guide specifies the purpose of different event logs. It states for the System log: "View system events such as device and network events, VPN status, and so on." This confirms it is the correct location for VPN status and related diagnostic messages. (Reference: Prisma SD-WAN Administrator's Guide, Chapter: Monitor, Section: Events).

2. Palo Alto Networks Prisma SD-WAN Administrator's Guide: In the troubleshooting section for VPNs, the standard procedure involves examining system events for detailed error messages. The guide explains that alarms like "VPNDOWN" are high-level indicators, and the root cause analysis requires inspecting the detailed logs generated during the connection attempt, which are found in Monitor > Events > System. (Reference: Prisma SD-WAN Administrator's Guide, Chapter: Troubleshoot, Section: Troubleshoot VPNs).