For some reasons I can't reply anymore to this thread and my problem is still not solved
https://www.voobly.com/forum/thread/354555/4

In short: yes I have IPv4, port forwarding are set up correctly, I have DSL. Still, I'm FP for 90% of players.

Could you please set this to UDP 29000:
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And also change the forwarded port to UDP 29000. Please upload a screenshot after.

Run network diagnostics again.

Non-DirectPlay game path is 'C:\Program Files (x86)\Microsoft Games\Age of Empires II'
Verifying 'C:\Program Files (x86)\Microsoft Games\Age of Empires II\language_x1.dll' exists...
Success!
Verifying 'C:\Program Files (x86)\Microsoft Games\Age of Empires II\age2_x1\age2_x1.exe' exists...
Success!
Voobly path is 'c:\program files (x86)\voobly'
Game version is '1.0C'
Verifying 'C:\Program Files (x86)\Microsoft Games\Age of Empires II\language_x1_p1.dll' exists...
Success!
Checking DirectPlay libraries...
Looking for dpwsockx.dll...
Looking for dplayx.dll...
'c:\windows\system32\dplayx.dll' size: 215552 bytes
DirectPlay Init Success!
Scanning installed DirectPlay games...
Age of Empires II
Age of Empires II - The Conquerors Expansion [found]
Game was found in DirectPlay registry!
DirectPlay play thinks the game is installed at 'C:\Program Files (x86)\Microsoft Games\Age of Empires II'
DirectPlay command line is 'Lobby'
DirectPlay play thinks the game exe is at 'C:\Program Files (x86)\Microsoft Games\Age of Empires II\Age2_X1\age2_x1.exe'
Verifying file exists... Success!
DirectPlay play thinks the language dll is at 'C:\Program Files (x86)\Microsoft Games\Age of Empires II\language_x1.dll'
Verifying file exists... Success!
Scanning 'c:\program files (x86)\voobly\gamedata\AOC\age2_x1.exe'
Success!

Everything looks fine. DirectPlay is configured and the game was found on your harddrive. If you still have problems try rejoining the lobby or restarting your computer.

For some reasons, I cannot change the port forwarding rule anymore. It says to enter a valid IP address. This is the address I get with IPconfig under IPv4.

Just type 99 there, it should auto complete it.

Same issue.

Starting networking diagnostics...

Your local network port (UDP) is 29000. All game traffic is routed through this port. This can be changed in "Settings" -> "NAT Traversal".

Attempting to connect to 3 test servers. This will take around a minute to complete...

Received data from 'server 3' through port 28727 (this is your WAN or router port)
Received data from 'server 1' through port 25637 (this is your WAN or router port)
Received data from 'server 2' through port 23472 (this is your WAN or router port)
14 seconds left.
9 seconds left.
4 seconds left.

Test Result: Symmetric NAT
Network Health: Poor
Recommended Action: Port forwarding recommended or switch routers. The only port you need to forward is UDP port 29000 on Voobly you do NOT need the direct play ports 2300-2400 and 47624.
Details: Your router assigned different public ports to all the test servers this will make it hard for users to directly connect to you. You will likely see a large number of fast proxies.

For help understanding this report or for more information go to http://www.voobly.com/pages/view/177#Network_Diagnostic_Tool.

I don't remember whether I asked this before, could you please check whether your router's firmware is up to date? Thanks.

It is.

Everything has been configured properly. If it's still not working I suggest you call your ISP. The port forwarding rule definitely isn't working at your end.