PRTG – P15 Monitor PRTG Server Downtime Using UptimeRobot (Internet Outage Case)

Monitoring systems are powerful — until the internet goes down.

If your PRTG server is hosted inside your company network, and your ISP connection fails, PRTG will not be able to send alerts. This creates a blind spot during the most critical moment: a full internet outage.

In this guide, we solve that problem using an external UptimeRobot monitor to track PRTG availability from outside your network.

This setup is lightweight, free, and highly effective for detecting internet downtime scenarios.

📌 Why You Need External Monitoring for PRTG

When PRTG is deployed on-premise:

• If the internet goes down → PRTG cannot send email alerts

• If firewall blocks outbound traffic → no notification

• If ISP fails → no external visibility

An external uptime monitoring service ensures you still receive alerts even when your internal monitoring system is unreachable.

This is where UptimeRobot monitor becomes extremely useful.

🆓 UptimeRobot Free Plan Overview

Free Plan includes:

• 50 Monitors
• Check every 5 minutes
• Email + App Push

Recommendation

Because it is a free plan, it has limited features:

• Maximum 50 hosts

• Minimum check interval is 5 minutes

• Faster intervals require a paid plan

Therefore, UptimeRobot Free is best used to detect:

• Company internet down

• PRTG server unreachable from the internet

If the company internet is down and PRTG is located inside that site, PRTG cannot send alerts — but UptimeRobot can.

#1️⃣ Step 1: Register an Account

Registration link:

Create a new account and verify your email.

Once logged in, you will see the dashboard where monitors can be added and managed.

This process takes less than 2 minutes.

#2️⃣ Step 2: Create an Uptime Monitor

Click Add New Monitor

You now need to choose the appropriate Monitor Type.

There are two recommended types depending on what you want to detect.

🔐 Monitor Type: HTTPS

Choose:

Monitor Type: HTTPS

Set the monitoring URL to your public PRTG web interface.

📌 Benefits

• Distinguishes:

o Web service down

This method checks:

• If your public PRTG web interface is reachable

• If HTTPS service is responding correctly

• If SSL handshake is working

If:

• Web service crashes

• IIS/Nginx fails

• Port 443 is closed

Then the HTTPS monitor will trigger an alert.

⏱ Interval Limitation

Set maximum 5 minutes.

Less than 5 minutes requires a paid subscription.

This means detection delay may be up to 5 minutes on the free plan.

🌐 Monitor Type: Ping

Choose:

Monitor Type: Ping

📌 Benefits

• Distinguishes:

o Server/Internet down

Ping monitoring checks:

• If the server IP responds

• If internet connectivity is available

• If routing is functional

If:

• ISP connection fails

• Server is powered off

• Network routing breaks

The Ping monitor will go DOWN.

⚠ Important Requirement

Firewall must allow ping.

If ICMP is blocked at firewall level, UptimeRobot will always detect the host as down even if it is online.

Make sure to allow ICMP Echo Request from the internet to your public IP (if security policy allows it).

🆚 HTTPS vs Ping – Which One Should You Use?

Best practice:

Use both monitors.

This allows you to distinguish:

• Web service down (PRTG service problem)

• Entire server or internet down (infrastructure problem)

Combining both gives clearer root cause analysis.

🚨 How Alerting Works

When a monitor changes state:

• UptimeRobot sends Email notification

• UptimeRobot sends App Push notification

Because UptimeRobot is cloud-based, alerts are sent even if your company internet is completely offline.

This creates a reliable external monitoring layer.

🏁 Real-World Internet Outage Scenario

Let’s simulate:

1. ISP cable disconnected

2. Entire company internet goes down

3. PRTG cannot send any email alert

Result:

• Ping monitor goes DOWN

• HTTPS monitor goes DOWN

• UptimeRobot sends alert to your personal email or phone

You now know immediately that the issue is external connectivity — not PRTG malfunction.

🔎 Architecture Concept

Internal Monitoring:

PRTG → monitors servers, switches, services

External Monitoring:

UptimeRobot monitor → monitors PRTG public availability

This layered monitoring approach prevents blind spots.

🏁 Conclusion

Using an external UptimeRobot monitor is a simple but critical enhancement for any on-premise PRTG deployment.

The Free Plan is limited, but sufficient for:

• Detecting internet outage

• Detecting PRTG web service failure

• Providing external confirmation of downtime

When PRTG cannot alert you, UptimeRobot can.

This small addition dramatically increases monitoring reliability and ensures you are never completely blind during an outage.