Add more information about port forwarding

Add image and mention that only TCP port can be checked using 3rd party
webpage

1 files changed, 7 insertions, 1 deletions

diff --git a/docs/hosting-a-server-with-northstar/prerequisites.md b/docs/hosting-a-server-with-northstar/prerequisites.md
index d2184c3..ce2cdd2 100644
--- a/docs/hosting-a-server-with-northstar/prerequisites.md
+++ b/docs/hosting-a-server-with-northstar/prerequisites.md
@@ -43,6 +43,12 @@ to your PC that you're running Northstar on.
 To check whether you set everything up correctly, start the game via Northstar and go into a private match. Another Northstar user should now be able to see your server on the server browser and join it.\
 You can also use a web based server browser like the one made by [Taskinoz](https://taskinoz.com/northstar/) or [cpdt](https://cpdt.dev/northstar/) to see if your server shows up in there.
 
-You can also use a third-party site like [this one](https://www.ipfingerprints.com/portscan.php) to see whether you set up port forwarding correctly by performing a scan while your Northstar server is running.
+You can also use a third-party site like [this one](https://www.ipfingerprints.com/portscan.php) to see whether you set up the TCP port forwarding correctly for the authentication port (usually `8081`) by performing a scan while your Northstar server is running.
+
+![Example check](https://raw.githubusercontent.com/R2Northstar/NorthstarWiki/main/docs/images/portforwarding-testing.png)
+
+![Working portforwarding for the TCP port](https://raw.githubusercontent.com/R2Northstar/NorthstarWiki/main/docs/images/portforwarding-working.png)
+
+Testing port forwarding like this only works for the TCP port due to the way UDP and Northstar work.
 
 Note that by default your server is called `Unnamed Northstar Server`. You can change this name as described in the next page.