Quick tips: custom port speed sensor for PRTG

We use PRTG Network Monitor at the College to monitor devices right across the network, from switches and firewalls right down to host \ VM \ application level for servers.

Recently I started playing a bit more with the network maps to try and build some “living” documentation that would give us live traffic stats whilst also satisfying the requirement of having some up-to-date network diagrams.

Port speed

Adding the devices and links was simple enough but we also wanted to display the uplink speed. Partially as it’s handy to visualise what goes where and also from a practical point of view to check if a link degrades.

However I couldn’t find a straightforward option to do this. It seemed possible as PRTG does actually display the speed when selecting ports to monitor but then doesn’t make the data available as a channel once added to the Devices list 😦

A bit of research confirmed I wasn’t going mad:

Ref: https://kb.paessler.com/en/topic/14843-how-to-see-port-speed-on-switches

Having the speed on the port name is nice but that’s a bit too wordy to be able to spot from a distance and being a text label isn’t really something that could be “monitored” if the value changes. However the comment about “ifSpeed” did give me an idea…

Custom library time

I’d already used the PRTG MIB Importer quite a few times bringing in libraries for various devices on the network so wondered if there was a value I could use to make a custom sensor. There was nothing in the device specific files for our switches so I figured that the value must be more generic \ standard than that.

Soon found this very handy website that walks through the SNMP OIDs; lo and behold there’s the ifSpeed values!

Ref: http://cric.grenoble.cnrs.fr/Administrateurs/Outils/MIBS/?oid=

Well in fact it’s a slightly different value called ifHighSpeed, the reason why it’s required for 10GB interfaces is referenced below:

“That is because when using ifSpeed, the output value will exceed the max. value (4,294,967,295)  that the object can support.”

Ref: https://supportforums.cisco.com/discussion/11124321/what-should-be-ifspeed-and-ifhighspeed-2-gig-interfaceport-channel
Ref: https://kb.juniper.net/InfoCenter/index?page=content&id=KB9119

After trying out the values using the free Paessler SNMP Tester along with the MIB Importer eventually brought me to the setup below, which has a nice little bonus of also showing the port’s name when selecting it in PRTG for easier identification. Note the other OIDs to obtain port name etc.

Once done it’s then a simple matter of saving the newly created file for use in PRTG and adding an SNMP Library sensor in to a test device.

Once added the sensor displays like this (port name can be changed as required)

Map display

The sensor was working well at this point but there was one final tweak required before getting the display I wanted. PRTG’s default template for a value-only map item adds the device’s name to the label, which in our case made for quite an unsightly string of text that got in the way of other map elements.

The solution? Go to your PRTG folder which looks something like

*install path*\PRTG Network Monitor\webroot\mapobjects
  • copy the item template in question, in this case it was “An icon B2.html” and name it as required.
  • edit the copied file to remove the “ParentDevice” string highlighted below.
  • also note you need to change the display name at the top of the file to something unique

Compare the before and after shots below:

original PRTG file

updated file with name edited and ParentDevice string removed

Once done open up the PRTG Administration Tool then restart the Core Server Service as per screenshot below:

End result

Now when you look in your map icons you’ll see the additional option appear as you named it above.
Drag that in and you’ll get the output in the format below, nice and clean 🙂