pfSense

Submitted PR: https://github.com/pfsense/pfsense/pull/3953

The 86400 limit is likely a holdover from when it used to be seconds, but letting it go up to a full day seems like it wouldn't be very useful in practice. I'd say the highest it should go should maybe be around 30-60 minutes.

Beyond that, the check can be disabled so the gateway is assumed to be up, which is better for backup cellular WANs since it wouldn't send any checks. If it's a PPP device on the firewall you can see the up/down status in the interfaces widget/status since it would show the login uptime. If it's a device that exposes the connection as Ethernet that's trickier.

I can modify it down to 3,600,000 ms (60 minutes) in the PR, if that works.

I'll be honest, I didn't really have a maximum value in mind. I saw the existing value and thought "oh, they must have meant 86400 seconds, because that's a full day," and tacked on three zeroes. I do agree that a monitoring interval that long would have limited real world value. I'll bring the value down to 60 minutes.

Change committed to the PR branch.

On 2.4.4.a.20180705.0032 you're able to set the probe interval to a max value of 36000000 as expected.