This is heavily borrowed from PingPlotter's own troubleshooting guide at Troubleshooting with PingPlotter.
Go to https://www.pingplotter.com/download and download PingPlotter for Windows. It is free to use when just running plots so you do not need to pay for a license.
Trace to a Server in the appropriate Server Farm
Enter a server name in the Target Entry field for the server farm that you wish to test the connection. A list of servers in each farm can be found on the support page, What ports does iRacing use. You do NOT need to worry about choosing the specific server you are connected to when racing. You only need to pick a server within the same farm. Typically, the servers to use for each farm are:
Click the green arrow on the right side to begin the trace. Once it is running, you should enter a practice session on the farm you are testing.
Record and Send Results
In most cases, your main focus should be the status of the final hop (the iRacing race server). Think of it this way: If packets are arriving at their destination quickly and safely, does it matter what happens to them along the way? The problems impacting the target are the problems impacting you, and finding where they begin is the ultimate goal.
PingPlotter has several ways to save and share the data you collect. The easiest is to save your session as a PingPlotter sample set file (.pp2). In the file menu, highlight “Export Sample Set” You can choose to export just the data in your focus period or export all the data you’ve collected for the current trace. The sample-set file can then be loaded in PingPlotter for you and others to review.
If pictures are more your thing, you can select “Save Image…” from the file menu to save a screenshot of your current target window graph.
Please include the pp2 file and if possible a screenshot as well when submitting an issue related to connectivity.