Reaching a service on Windows from inside WSL — sometimes localhost works, sometimes it does not, and I cannot see the pattern Networking

For question 2, use the address the distro already knows, rather than localhost. Inside Linux:

ip route show default | awk '{print $3}'

That gives the gateway, which is the Windows host on the virtual network. It changes on every restart, which is exactly why hardcoding it into a config is a bad afternoon.

So do not hardcode it. Options in order of how well they hold up:

• Resolve $(hostname).local if your setup provides it
• Read the gateway at startup in your app's config
• Switch WSL to mirrored networking mode, in .wslconfig:

[wsl2]
networkingMode=mirrored

Mirrored mode makes the distro share the host's network interfaces, so localhost genuinely means the same thing on both sides in both directions. It is the real fix for your problem rather than a workaround, and it also tends to survive VPNs, which the shim does not.

The asymmetry is the whole answer, and it exists because only one direction has special handling.

In its default networking mode the distro is a virtual machine on its own network, with its own address. Two separate hosts.

Linux → Windows gets no help. There is a forwarding shim that makes localhost work, but it is doing translation on the fly and it is the fragile half — VPN clients, a firewall profile flipping to Public, third-party network filters and some corporate agents all break it. That is your laptop.

Windows → Linux is the direction that gets real support: when something inside the distro listens on a port, Windows publishes it on localhost automatically. That is why it never fails for you.

So it is not that one is broken. It is that one is a convenience layer and the other is a supported feature.