Issue in one of our sites: One of the 2 delivery controllers suddenly throws these errors: After the error is thrown, the server is unavailable, no contact with the domain or the other DDC. The site is unavailable, as the other DDC doesn't pick up that there's an issue somehow. After reboot, everything is OK. Has happened on the same site a couple times the last months now, we even tried replacing the DDC's with new servers, but issue remained.

I have occasionally seen this, but never on a delivery controller. If you can't get to the root cause you could increase the dynamic port range. https://learn.microsoft.com/en-us/troubleshoot/windows-client/networking/tcp-ip-port-exhaustion-troubleshooting

I have seen that Event 4231 on our cloud connectors before but it was during other Citrix issues and it was more the result of something else not working and not THE problem if that makes sense. Let me see if I can find any notes on that as it was a quite a while ago.

Thanks, I've set up a task that dumps netstat -anob to a file every 15 minutes, so hopefully I'll be able to find the perpetrator

i have a handy powershell script i have used in past when looking at a port exhaustion issue

It just happened on one of the controllers (the one i didn't set up logging on of course..), after restart i'm seeing a lot of established TCP connections between the controllers on the citrix.exe process. Not seeing this elsewhere.