Alerts are being fired when the tunnel had been down for less than 30 seconds.
How to configure Infrastructure Manager to alert only when a tunnel has been down for at least 5 minutes?
CA UIM hub/tunnel
In the hub GUI select Tunnels -> Advanced Tab: 'Tunnel is hanging Timeout' and set it to 300 seconds (5 mins).
This setting determines when the tunnel disconnect alarm is generated.
For hubs without a tunnel connection, no alarms will be sent if an other hub goes down.
The best way to to monitor other hubs is to use the net_connect probe to check if the NimBUS_HUB service (port 48002) is responding.