How To Create Lan Server Assetto Corsa

Question Can't connect to game server locally

Thread starter Airnub
Start date May 4, 2020

: Oct 18, 2019

: 6

: 0

: 10

: 0

I'm having some trouble with setting up a dedicated server for a game called Assetto Corsa. I've forwarded the ports needed and I can see the server listed in the serverlist. But when trying to join a mp server on AC you have to select a car before you can join the server. And the list of cars available on my server does not show up on my local network. I've tried with several computers. I've also run the server from different computers without solving the problem.
But if I change the http port on the server. And forward the new port. I can select a car and join the server within the 5 or so minutes after starting it again. People from outside my home can join at any time

: Aug 9, 2012

: 23,167

: 1,531

: 114,690

: 7,290

I have not heard of that game so I can't say how it works.

Do you have the option to access the local server using its local lan IP rather than using the external IP of your router.

This sounds like the common problem called NAT HAIRPIN. As part of the communication your pc sends it traffic to the router and the source IP address is mapped to the external IP. This is standard NAT. BUT the destination IP is already set to the same external IP so the traffic needs to be send back it. In theory it should translate the destination IP to the settings you made in the port forwarding.

If it sounds confusing think about the router. You have both the source and destination ip addresses set to the same value but they translate into different internal IP. Even worse when the traffic goes back the other way the source and destination are now reversed and the router must keep all the straight.

Not all routers even attempt to do this. The ones that do not not even document they do. Since it appears to work sometimes it might be a limitation on the implementation.

The best is to avoid the issue and use the local lan ip rather than the external. If you are using a DDNS name you can also put a HOST entry into your PC that over rides the DNS and point it to the local lan IP rather than using the ip it gets from the DNS.

Problem maybe is if the machine that has the server list tells yous machine to use the external IP you can't fix that. I bet if you were to use a VPN it would work fine.

: Oct 18, 2019

: 6

: 0

: 10

: 0

I have not heard of that game so I can't say how it works.
Do you have the option to access the local server using its local lan IP rather than using the external IP of your router.

This sounds like the common problem called NAT HAIRPIN. As part of the communication your pc sends it traffic to the router and the source IP address is mapped to the external IP. This is standard NAT. BUT the destination IP is already set to the same external IP so the traffic needs to be send back it. In theory it should translate the destination IP to the settings you made in the port forwarding.

If it sounds confusing think about the router. You have both the source and destination ip addresses set to the same value but they translate into different internal IP. Even worse when the traffic goes back the other way the source and destination are now reversed and the router must keep all the straight.

Not all routers even attempt to do this. The ones that do not not even document they do. Since it appears to work sometimes it might be a limitation on the implementation.

The best is to avoid the issue and use the local lan ip rather than the external. If you are using a DDNS name you can also put a HOST entry into your PC that over rides the DNS and point it to the local lan IP rather than using the ip it gets from the DNS.

Problem maybe is if the machine that has the server list tells yous machine to use the external IP you can't fix that. I bet if you were to use a VPN it would work fine.

There's no option to connect by ip. So you can only connect to servers listed in either the "internet" tab. Or the "lan" tab. But since my server is set to internet I can't find it in the lan tab. I've actually had a guy working for my ISP take a look at both my router settings and my server settings. And he couldn't find anything wrong. So I don't know what to do to make this work.

: Aug 9, 2012

: 23,167

: 1,531

: 114,690

: 7,290

This is where not knowing the limitation of the game I can't say if you can make changes to the game server to fix this. If there is a game forum see if someone knows what HAIRPIN NAT means and if they have a fix for it.

The router you can't generally change anything. The hairpin nat feature ether just works or it does not.

Your best option is likely going to be a VPN so that your traffic is actually coming into your router from a different ip address.

If you really want to learn lots about how NAT REALLY works you might be able to load dd-wrt on your router. You can then write your own rules for how this nat is done. It is done in a file called IPTABLES and it makes your head hurt to learn. Who ever invented this method of putting rules in I think likes to smash his fingers with a hammer.

: Oct 18, 2019

: 6

: 0

: 10

: 0

There's nothing I can do to the game or the server afaik. I've asked the devs of the 3rd party tool I'm running for help. But they don't seem to care. I can't do much other than change the SSID's and forward ports on my router. As the regular config is locked for the customers. If I want a static ip on one of my computers I need to call customer support. Or my buddy who works there

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