Monitoring network downtime with PRTG

I’ve been using MRTG for a while to monitor assorted servers, routers, and switches I manage at The Windmill. It’s free, works pretty well, and is quite configurable. The graphs it produces are plain but functional, and they do the job.

Recently, I needed a tool to monitor my home network, primarily because the Cisco 3925 router provided by my Internet supplier, UPC, has had a nasty tendency to lockup every week or so. Now, UPC’s 120 Mb/s Internet service is fantastic value, and performs exceptionally well, but having it randomly interrupted like this is really, really annoying — especially when the router is buried in a small cupboard at the back of our attic, where all the TV wiring is concentrated.

I also have a wireless access point (an old reconditioned Eircom Netopia 2247) which periodically hangs, though on a different schedule to the Cisco. So, I figured it was time to start monitoring both devices to see exactly when they go offline, in the hope that I might be able to correlate it with other network activity.

While MRTG can do this, it’s not the most user friendly of systems to configure. Since I crave nothing more than an easy life, I decided to look around for alternatives.

This brought me to PRTG, a commercial monitoring tool from Paessler that covers some of the same ground. It’s free for up to 10 monitoring points, runs under Windows, and has a nice web-based GUI that makes it easy to configure or review logs from anywhere on my LAN. So, I decided to give it a try.

I’ve been using PRTG for about two months now, and it’s working very well. There are a huge number of built-in sensors: everything from basic PING tests, SNMP polling of routers & switches to Windows system metrics (for any machine on the LAN) to remote website HTTP monitoring. With the 10 free sensors included in the evaluation copy, I was able to add rules for three websites I manage, my Wifi and Internet routers, a separate VPN router I use to access client networks, and also a few of my local machines:

PRTG lets you create sensor dependency trees: for example, I monitor the uptime of this website ( but the monitoring rule says not to try and monitor it if the UPC Cisco router is down, OR if Google’s main DNS server at can’t be reached. This ensures I don’t get an onslaught of website failures in the log just because my Internet connection was interrupted.

PRTG also lets you raise alerts whenever a sensor goes on or offline, or crosses a threshold. For example, if the disk space on C:\ on my main Media Center TV system drops below 1 GB, I can easily have PRTG alert me, either by email or SMS.

I’ve barely scratched the surface of what’s possible so far, but it’s a very capable system. When Paessler emailed me today with an offer to upgrade my free 10-sensor license to 30 sensors in return for some blog coverage, it wasn’t a difficult decision. While I only blog about products I actually like and use, PRTG now falls squarely into that camp. Give it a try and see what you think for yourself.