Port 16262 closed warning but it´s opened correctly

[Major]

So I seem to be getting the port 16262 is closed, performance might be severely affected warning when connecting to my server.
The server is installed through steam cmd and I try to connect from a client started through steam (using the ingame server browser/entering the IP manually).

Port 16262 is opened for UDP connections and I have verified that it is indeed open by shutting down the server and listening 16262 UDP through netcat, then connecting from my local machine to the server (Hosted with an dedicated IPv4 address) and I can see my packets arriving meaning that server-side configuration (firewall) must be correct.
I tried with UPnP enabled and disabled but always get the same errors. 

Is there some way to debug the client and check if it´s actually trying to connect to 16262 or using some different port since online you´ll find ambiguous reports that it actually uses some range instead of this specific port or similar.

I tried the broadest port ranges I could find for now (I´d like to limit it back to the actual ports used once figured out) and this is my current UFW config
 

[project_zomboid]
title=Project Zomboid
description=Project Zomboid server ports
ports=16262:16293/tcp|27015/tcp|27036/tcp|8766:8767/udp|16261:16262/udp|27015/udp|27031:27036/udp

 

Also netstat shows that 16262 is indeed bound:
 

major@vmd106028:~$ netstat -a | grep 16262
udp        0      0 0.0.0.0:16262           0.0.0.0:*

 

Edited January 26, 2023 by Major

[Beard]

I am not familiar with any specific service that checks for UDP ports, though if the game tells you that it is closed then it would indeed be likely closed. Did you make sure to port forward the port through your firewall and router? Specifically the UDP protocol. Preferably do not use ranges, as some routers might have issues with those.

[Major]

Well, the server is a hosted root-server with a dedicated IP in a server-cluster. There are no real firewalls in that sense, all traffic is routed to my server.
Then, there´s the UFW firewall running inside my Ubuntu distro where I host the server. The UFW firewall is open for 16262 on UDP (as well as 16261).
NMAP or NetCat can be used to test UDP packets. You basically install it on the host that you´re trying to test, let it bind to port 16262 (that´s why the PZ server must be shut down) and then you try to send an udp packet using another netcat instance towards the server from a remote machine. If you see some inbound traffic you can be sure that the port is forwarded.

Anyways, I´ll try to disable the firewall completely on this host and check if the connection works then.
Thanks so far, if I have some finding I´ll report back, maybe it helps some other users.

[Major]

So, I found the "solution".

I disabled the firewall completely meaning that all ports are fully exposed but the warning message was still shown. 
This looked very suspicious so I had a closer look at the client and I found that in the server browser/connection profile I had the steam relay enabled. 
I wonder why this is the case since when I add a new server the option is disabled by default it seems. However some other people playing on my server also reported to me that the steam relay option is enabled in the connection profile of their clients and they see the message. Neither them or myself remember enabling this option manually. 
Anyhow, once I unticked the checkbox the warning disappeared. Furthermore, I was able to limit the firewall to 16261 UDP and 16262 UDP only and everything works fine.

[EnigmaGrey]

Guess it makes sense: 16262 is the direct connection port; 16261 is the Steam port. So by forcing Steam relay only, it’d act like the direct port isn’t there.

 

So the bug is the message showing up when steam relay is selected.