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October 9, 2020

Connecting to Expo Dev Server in WSL 2 over LAN

This post drafts things I did to connect my Android device to Expo dev server running in WSL 2 on Windows 10 over LAN connection (in my case using Wi-Fi). The set-up looks like below:


Note: Expo-Client is installed on my android device.

Note: Expo-CLI npm version used is 3.27.14

Assumption: IPv4 address is used over IPv4.

When you run `ip address` in your WSL 2 terminal, you will your ip-address of your VM as something like  172.x.x.x.

When you check the ip address of your Windows 10 host, by running `Get-NetIPConfiguration` in your PowerShell terminal you will find your host ip to be something like 192.168.x.x. When you connect your Android device to the same LAN over Wi-Fi, your ip address would be similar (something like 192.168.x.x).

The fact that WSL 2 isn't sharing the same ip address as its host is an issue to be resolved. This needs to be fixed as first thing, because otherwise how do we even reach the server running in WSL over LAN? The easy fix to this is to prefix your server start command with your windows host ip like `REACT_NATIVE_PACKAGER_HOSTNAME=your_windows_host_ip`. In my case I run the expo server like `REACT_NATIVE_PACKAGER_HOSTNAME=192.168.10.12 expo start`.

Your expo server runs in port ranges of 19000-19006. Make sure your WSL firewall isn't blocking these ports. I have Ubuntu 20.x as my WSL 2 VM. I check to see if my firewall is active and if active are the mentioned ports listed and open by running the command `sudo ufw status verbose`. In my case the firewall status is inactive as expected. Note that using a firewall in WSL is redundant and should you choose to have it activated, you can add those mentioned ports using the command `sudo ufw allow $PORT`, where $PORT is the port number that you want to add to firewall rules to open it up.

You also need to do port forwarding of the mentioned ports on windows host operating system. You can use netsh on your Powershell in admin mode. The cookbook for it will be below commands:
  • List all your portproxy rules: `netsh interface portproxy show v4tov4`.
  • Remove all your portproxy rules: `netsh int portproxy reset all`.
  • Forward Ports into WSL2 :  use the net shell "netsh" to add a portproxy rule. Again, change connectaddress to YOUR WSL2 ipaddress, which is an internal address to your machine.
    netsh interface portproxy add v4tov4 listenaddress=0.0.0.0 listenport=19000 connectaddress=127.0.0.1 connectport=19000
  • Open The Firewall: Next, from the same Administrator Windows prompt, open an incoming Firewall Port. You can do it from the Advanced Firewall Settings, but even easier you can use netsh again!
    netsh advfirewall firewall add rule name="Open Port 19000 for WSL2" dir=in action=allow protocol=TCP localport=19000
In an ideal world this should get you going. In my case though, doing all these still didn't help me and I had to resort to tunneling and making use of expo's platform for this.


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