Hello,
=>
https://www.managames.com/tennis/doc/Te ... ml#networkthen =>
topic8-3102.phpIn short, the main advice is:
- try using UDP Port 80 instead of 4321 ; or try UDP Port 54321 instead of 4321
- turn off your Firewall
- alternatively, remove Tennis Elbow from your Firewall rules, so it will ask you again the next time you play online
- set your router to Forward all, or put your PC in DMZ (make sure your PC is secure before doing this) ; if that doesn’t help, try Bridge mode instead of Router mode (if your router supports it)
- check that your Windows Network is set to Private network, not Public network (Tutorial => http://www.opentechguides.com/how-to/ar ... -type.html ) ; or try allowing TE2013 through Windows Firewall even on a Public network
Update December 2020: (only for TE2013, not TE4)
If you don’t have a public IPv4 (i.e. either no IPv4 from your ISP at all, or a private IPv4 encapsulated within IPv4/IPv6 at your ISP level), then people using the server list won’t be able to join you.
You should still be able to play by giving your IPv6 directly to another player, who must enter it in the "Join Remote Game" IP field. (I think I tested this a decade ago, so not 100% sure it still works

)
Update March 2022:If you’re behind a
CGNAT, you’ll never be able to host.
Update May 2022:I ran into the dreaded "it was working before but now it doesn’t work". After a lot of checking, I found out that the UPnP IGD service of my Sagem router (Orange ISP) had stopped working..!

I fixed it by updating the firmware. Although it’s possible that simply
turning it off and on again would have been enough.

Alternatively, a factory reset might also have solved it.
Update April 2024:If TE4 offers to assign a Temporary IPv6, try it ; it might solve your issues (though people who only have IPv4 won’t be able to join you).
Alternatively, assigning your static IPv6 could make it easier to open the port in your router’s IPv6 firewall (note: this is not NAT/Port forwarding, it’s the actual IPv6 firewall). Again, people with only IPv4 won’t be able to join you.
Update September 2025:A new issue popped up: the game now uses IPv6 by default instead of IPv4 (no idea why

), and my Internet Box also added an IPv6 firewall that can’t be disabled.
So I had to manually allow the TE4 UDP Port in the Box’s firewall settings for my PC (make sure you select the right device in the list).
It’s extremely inconvenient because it’s not compatible with UPnP, so the game cannot configure it automatically for you.