Access a localhost running in Windows from inside WSL 2

Question

I am running a local AEM server in my Windows machine. The server is running on localhost:4502. I am using a Ubuntu distribution running in WSL 2 for my development. I want to access the localhost:4502 running in the Windows machine in my WSL 2 Ubuntu.

Is there a way to do that or is it not possible?

Answer 1

Short answer for most recent Windows versions

mDNS has been a feature of WSL2 for a while now. Concatenating your WSL2 hostname (or the equivalent command/function in your programming/language environment) with ".local" should get you access.

For example, from Bash, try:

ping "$(hostname).local"

For instance, if your hostname is "MyComputer", then the mDNS should be MyComputer.local.

If ICMP is blocked (as it seems to be on new Windows 11 installs), or if you want to test the connection to the actual port, then use netcat. It's available by default in the WSL Ubuntu installation, but may need to be installed in other distributions like openSUSE:

nc -zv "$(hostname).local" <portnumber>

Why localhost doesn't work

WSL2 is running with a virtual network (vNIC) that is created by the Windows Virtual Machine Platform (a subset of Hyper-V). Inside WSL2, localhost is the address of the vNIC.

What you need

WSL2 also sets up a virtual router on the Windows host to allow connectivity to both the outside world as well as the Windows host. You can see this via:

ip route

This is the address you need to use for the Windows host.

You could, of course, parse it from the route (or, as in an earlier answer, from /etc/resolv.conf), but WSL sets up a convenience mDNS (the .local domain) using the Windows "computer name", which is also used as the hostname of the WSL instance.

So concatenating $(hostname) (or it's equivalent in your programming/language environment) with ".local" should get you access.

Other considerations:

• mDNS is reliant on the Windows host to resolve the name. If you have changed your /etc/resolv.conf under WSL, then this will likely not work.

• Remember to open any necessary firewall ports. WSL2 is considered a separate network from that of the Windows host. Windows will consider network connections from WSL2 to be coming from an external source. (Credit to @RamilGilfanov for a comment pointing this out)

  The first time a connection is made from WSL2 to a particular port, Windows Defender (if that is your firewall) will typically display a dialog asking if you want to grant access. However, in my experience, this dialog often gets buried under the main window due to timing of mouse-clicks, keyboard, etc., so it's easy to miss.

• Remember to have your Windows service accept connections from remote hosts.

  Many servers are configured by default to bind to localhost/127.0.0.1. Because WSL2 appears to Windows as a remote network, you'll typically need to update your configuration to bind to 0.0.0.0 or a specific address.

  Note that, since the address for WSL2 changes after each reboot, it can be difficult to update your configuration each time. If at all possible, use 0.0.0.0 unless there are security concerns. Since WSL is designed for development rather than production, this shouldn't be an issue.

Answer 2

I was also looking for some solution to do this, but currently there isn't any such option available. Check out this GitHub issue:

[WSL 2] WSL 2 cannot access Windows service via localhost:port #4619

One solution can be this:

If you have the IP address of the Windows (host) then it will do the job, but the only problem is that the IP address will change every time. But, WSL 2 stores your Windows (host) IP address in the /etc/resolv.conf file. So we can modify our etc/hosts file to map winhost to the IP address dynamically.

Add the following lines at the end of the ~/.bashrc file file. This will grep the IP address and modify the etc/hosts file when you boot the WSL.

export winhost=$(cat /etc/resolv.conf | grep nameserver | awk '{ print $2 }')
if [ ! -n "$(grep -P "[[:space:]]winhost" /etc/hosts)" ]; then
        printf "%s\t%s\n" "$winhost" "winhost" | sudo tee -a "/etc/hosts"
fi

Then run the following command to reload the changes.

source ~/.bashrc

Now you can use winhost instead of localhost in WSL 2 (client) to access the servers running Windows (host). In your case, it will be winhost:4502, but this will work for any other use cases as well like accessing a PostgreSQL or MySQL server running on Windows, etc.

Note: Always remember to configure your firewall on Windows to allow those ports, so that WSL 2 can access it. Otherwise, your connection may get blocked by the firewall.

Answer 3

This is simple; you just need to do two things. Set the IP address to localhost in the hosts file and allow Windows Firewall to allow incoming connections.

Here are step-by-step instructions:

1. Get the IP address. Open cmd.exe and type ipconfig /all. Note down the IP address 172.22.16.1

   

2. Open Notepad as administrator, menu File → open, browse to C:\Windows\System32\drivers\etc\hosts, add the line 172.22.16.1 localhost, save and close.

3. The last option is to allow Firewall rules to accept public connections. For this, open Control Panel* → System and Security → Windows Defender Firewall → Advanced Settings → Inbound Rules → New Rule

4. Rule Type: choose Port and click Next

5. Protocol and Ports: type Specific local port: 4502, and click Next

6. Action: Allow the connection and click Next

7. Profile: check Public and click Next

8. Name: type AEM server and click Finish

9. Close other windows, and again open cmd. Type wsl --shutdown for shutting down the Ubuntu subsystem.

10. Open Ubuntu again.

11. Testing connection: type curl localhost:4502 in command prompt. If it returns something, it means you are good to go.

Answer 4

You need add an IPv6 rule in the hosts file.

Like:

127.0.0.1 example.com
::1 example.com localhost

I had a similar problem and found the solution at the page WSL 2 Linux host cannot be accessed by a custom domain name or 127.0.0.1 #5728.

Answer 5

The easy way:

On the Ubuntu command line, type:

ip route

Output:

default via 172.23.96.1 dev eth0
172.23.96.0/20 dev eth0 proto kernel scope link src 172.23.97.122

In your application, configure the host to: 172.23.97.122

Now you can access it using Windows Browser.

Answer 6

Windows 10 considers localhost as ::1. Ubuntu considers localhost as 127.0.0.1.

So solution is to create a mapping. Create a file called *.wslconfig* in C:\Users\<your_username>\.wslconfig.

Add the following to it.

[wsl2]
localhostForwarding=true

PS: I don’t know if it messes up anything else, but it helped me run Django servers which were broken after upgrading to WSL 2.

Answer 7

I suspect you could do this.

1. Step 1. Run your AEM server on your actual IP address (or all addresses) instead of binding to just localhost.

2. Step 2. Your Ubuntu WSL client instance won't share localhost with the host machine, but it will share the local IP address your machine actually has (e.g. 10.0.0.2). Just have your client connect to that IP address instead of localhost.

3. I don't know anything about AEM, but you might need to secure it if you are exposing it to a larger network. Block port 4502 on the upstream firewall or use a Windows Firewall rule to only allow incoming on port 4502 from your own IP address. This certainly appears possible.