As of release 2.0.0 of WSL2, there is a new networking feature available that circumvents the need for almost all of my original answer. That said, both techniques are still useful. I'm revising this answer to list the new mode ("Mirrored Networking") first.
Mirrored Mode
Note: Only available in release 2.0.0 of WSL2 with Windows 11 22H2 or higher
In this mode, the Windows network interfaces are mirrored into WSL2. When you run ip addr, for example, you'll see (mostly) the same interfaces as when you run ipconfig /all from PowerShell/CMD.
As a result, this negates the need for the three items mentioned in the NAT section:
localhost can be used from WSL2 to connect to the loopback address for Windows- Firewall rules between Windows and WSL2 are not needed 1, since Windows will see WSL2 traffic as "local"
- The bind address for your Windows service can still be the localhost address, rather than
0.0.0.0
To enable Mirrored mode:
Add the following to your <windows_user_profile>/.wslconfig:
[wsl2]
networkingMode=mirrored
Exit your WSL distribution
Run wsl --shutdown from PowerShell then restart WSL
You should then be able to access services running in Windows via localhost.
Note that when running in Mirrored mode, mDNS will not work.
NAT (default/original) Mode
To access a network service/application running on the Windows host from inside WSL2, you need to do three things:
*Configure the service to listen on the correct Windows network interface (not localhost), a.k.a. the "bind address".
Open the necessary firewall port(s)
Use the correct address from WSL2 (again, not localhost)
For you, the OP of this question, it appears that you already had the 2nd and 3rd correct, and only need to change the first.
More detail provided below on each of these:
Bind address
Many applications or services default to binding to localhost, which (obviously) means that you can only connect to them from the host on which the service is running. Because WSL2 runs on a "separate network", you won't be able to access the a service that in Windows that is listening only on localhost. As @DanielB mentioned, you'll probably want to bind to 0.0.0.0 (for IPv4) and/or :: (for IPv6) to listen on all interfaces.
The method of configuring the service will, of course, vary for different applications, but usually you'll find the setting labeled something like "Bind Address", "Listen On", or something similar.
Make sure to restart the application/service after changing this setting.
Firewall configuration
By default, Windows Defender Firewall (and others) will block incoming connections to the host from another network. Since we've already established that WSL2 is running in a separate network, you'll need to open a firewall port for your service.
The OP of this question has disabled the firewall entirely when coming through the WSL2 network interface, which is fine. You can also do this selectively from PowerShell (in an Administrative shell) with something like:
New-NetFirewallRule -DisplayName "Spring App Testing" -InterfaceAlias "vEthernet (WSL)" -Direction Inbound -Protocol TCP -LocalPort 8545 -Action Allow
Of course, you can drop either:
- the
InterfaceAlias, in which case it will open 8545 from all networks
- or the
LocalPort, in which case it will act like the "disable" option above and always accept incoming traffic from the WSL network interface.
Finding the correct Windows address to use from WSL2
There are several methods (and IP addresses) you can use. The easiest way is simply to use the IP address of the Windows host, if you know it. However, if it is dynamically assigned and changes frequently (which is, I believe, fairly unusual nowaways), then you may need to change your WSL2 code each reboot.
It's probably best, however, to use a mDNS name that will (usually) resolve correctly.
Assuming that you haven't overridden the default /etc/resolv.conf that WSL generates, this can be done by taking the Windows computer name and simply appending .local. For instance, if your computer name is bubblegum, then bubblegum.local should be the correct address.
You should find that this is the same address as found with:
echo $(ip route list default | awk '{print $3}')
If, however, you have overridden the /etc/resolv.conf (necessary in some cases due to VPNs or other networking configurations), then you may need something more complicated like:
echo $(host `hostname --long` | grep -oP '(\s)\d+(\.\d+){3}' | tail -1 | awk '{ print $NF }' | tr -d '\r')
(Credit to @ChaiAng's answer on Ask Ubuntu for this method).
However, note that it is substantially slower than mDNS.
1 Note that Mirrored mode also makes your WSL2 instance available to other devices on your network, and for this reason, there's also a new WSL2/Hyper-V firewall feature that, by default, blocks that traffic. Enabling traffic between the local network and WSL2 is a different topic.
