vpnparty

A LAN party via VPN. Allows games to discover each other through VPN like if they were in local network.

Verified games

Game	Version	Port	Status	Note
Titan Quest	2.10.21415	42801	✅
Torchlight 2	1.25.9.5	4549	✅
Warcraft 3	1.26.0.6410	6112	✅	Original (not reforged) Frozen Throne and Reign of Chaos
Chicken invaders 5	5.0.0.0	23016	❌	I suspect that game has checks whether the packet is broadcast.

How to use

1. Download and install latest Npcap. Tested with versions 1.79, 1.80 and 1.87. Any compatible should fit. Important! Select Install Npcap in WinPcap API-compatible Mode checkbox!
2. Compile or download binaries from release page. See compilation instruction below.
3. Add vpnparty to your firewall exceptions. It needs UDP ports 54928 and 54929 by default.
4. Run vpnparty without arguments. Just double-click. Should work as is.

CLI options

You can adapt application behavior to your needs. Let's see some examples:
.\vpnparty --help shows detailed help message with examples.
.\vpnparty -b 10.0.0.15 10.0.0.22 manually specify peer IP addresses.
.\vpnparty -b 10.0.0.15 10.0.0.22 --no-multicast --no-udping if you know all your peers (let's say there are 3 players), feel free to disable both discovery mechanisms as redundant.
.\vpnparty --monochrome is useful if your command line doesn't support color output.
.\vpnparty -p 7654 retransmits only broadcast packets with destination port 7654. Useful if you know exact port that your game uses. By default all broadcast packets are retransmitted, which might be not desired. One more option is -p known, which is the synonym to -p 4549 6112 42801. See those ports in Verified games section.
.\vpnparty -v=1 to see debug messages. Set -v=2 to see all processed packets. Useful for debug.

How it works

Expert option: specify friend's IP manually, disable discovery protocols. Your friend doesn't need to run vpnparty at all. .\vpnparty.exe -b 10.0.0.2 --no-multicast --no-udping

sequenceDiagram
    participant w1 as PC 1<br/>IP: 10.0.0.1<br/>Warcraft 3
    participant v  as PC 1<br/>IP: 10.0.0.1<br/>vpnparty
    participant w2 as PC 2<br/>IP: 10.0.0.2<br/>Warcraft 3
    Note over w1: Original packet:<br/>Dst IP: 255.255.255.255<br/>Dst port: 6112
    w1-->>v: Broadcast packet<br/>intercepted by npcap
    Note over v: Rewrite the packet header:<br/>Dst IP: 10.0.0.2<br/>Dst port: 6112
    v->>w2: VPN connection
    Note over w2: Reply packet:<br/>Dst IP: 10.0.0.1<br/>Dst port: 6112
    w2->>w1: Game reply via VPN connection

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Regular option: no arguments, vpnparty runs on both sides, rely on autodiscovery. .\vpnparty.exe

sequenceDiagram
    participant w1 as PC 1<br/>IP: 10.0.0.1<br/>Warcraft 3
    participant v1 as PC 1<br/>IP: 10.0.0.1<br/>vpnparty
    participant v2 as PC 2<br/>IP: 10.0.0.2<br/>vpnparty
    participant w2 as PC 2<br/>IP: 10.0.0.2<br/>Warcraft 3
    v1-xv2: Multicast request (port 54929, assume failed)
    v1->>v2: UDP request (port 54928)
    Note over v2: Peer discovered at 10.0.0.1
    v2->>v1: UDP reply (IP 10.0.0.1, port 54928)
    Note over v1: Peer discovered at 10.0.0.2
    Note over w1: Original packet:<br/>Dst IP: 255.255.255.255<br/>Dst port: 6112
    w1-->>v1: Broadcast packet<br/>intercepted by npcap
    Note over v1: Rewrite the packet:<br/>Dst IP: 10.0.0.2<br/>Dst port: 6112
    v1->>w2: VPN connection
    Note over w2: Reply packet:<br/>Dst IP: 10.0.0.1<br/>Dst port: 6112
    w2->>w1: Game reply via VPN connection

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How to compile

1. Download Npcap SDK (tested with version 1.13 and 1.16). Unpack wpcap.lib for your platform.

curl -L -o npcap-sdk-1.16.zip https://npcap.com/dist/npcap-sdk-1.16.zip
tar -xvf npcap-sdk-1.16.zip Lib/x64/wpcap.lib

2. Set LIBPCAP_LIBDIR environment variable to point to folder with wpcap.lib for your platform. Use one of those methods:

• $Env:LIBPCAP_LIBDIR = "C:\path\to\npcap-sdk-1.16\Lib\x64" (temporary changes)
• [System.Environment]::SetEnvironmentVariable("LIBPCAP_LIBDIR", "C:\path\to\npcap-sdk-1.16\Lib\x64", "User") (permanent changes)
• Edit the system environment variables → Environment variables → System variables → New

3. Clone and build repository.

git clone git@github.com:tvladyslav/vpnparty.git
cd vpnparty
cargo build --release
cargo clippy --all-targets --all-features -- -D warning

4. target\release will contain generator.exe and vpnparty.exe.

• generator.exe is the debug tool. It sends 2 broadcast packets (to ports 4549 and 6112) every second. See troubleshooting section for details.
• vpnparty.exe is the application that you need.

Troubleshoot

Q: LINK : fatal error LNK1181: cannot open input file 'wpcap.lib' A: Please download Npcap SDK. Extract. Then create LIBPCAP_LIBDIR environment variable, which points to npcap-sdk-1.16\Lib\x64.

Q: wcap.dll was not found
A: Reinstall npcap and remember to select Install Npcap in WinPcap API-compatible Mode checkbox.

Q: I see the There are active virtual network adapters in your system. warning.
A: Please follow recommendations of the warning. As alternative, go to Control Panel\Network and Internet\Network Connections and disable devices with "v" prefix (like vEthernet). Virtual devices can capture game packets, they won't reach vpnparty and your peer as the consequence.

Q: I run application but still can't join friend's game lobby. Why?
A: Several suggestions:

1. Go to Control Panel\System and Security\Windows Defender Firewall\Allowed apps and allow vpnparty. Allow the app in any other firewall in your system.
2. Make sure that vpnparty discovered the peer. You should see the line like <IP> joined the party!. vpnparty can't resend packets to nowhere.
3. Turn on packet tracing using .\vpnparty -v=2 flag. You should see all captured packets, where first letter denotes: B = resent game-related broadcast packet, M = multicast peer discovery, U = UDP peer discovery.

Acknowledgements

Thanks Ratmir Karabut and his udp-broadcast-tunnel for inspiration.

License

GNU GPLv3