Reports the result of the gateway's own link-probing mechanism, Tunnel Testing or RDP-based link status probes, for this tunnel: whether the probe currently sees the tunnel as alive, dead, or unknown. This is distinct from tunnelState, which reflects IKE and IPsec negotiation state, because a tunnel can be fully established at the IKE layer yet have its actual data path silently fail; tunnelProbState is what catches that up-but-not-actually-passing-traffic condition. Example: a tunnel showing tunnelState active(3) but tunnelProbState dead(2) is the classic signature of a tunnel that negotiated successfully but whose data path has since broken, which failover logic uses to trigger a switch to a backup link.