Mirrored Networking - 0.0.0.0 Bind Problem (Not Mirrored Correctly)

Windows Version

Microsoft Windows [Version 10.0.26100.3194]

WSL Version

2.4.12.0

Are you using WSL 1 or WSL 2?

• WSL 2
• WSL 1

Kernel Version

Linux version 5.15.167.4-microsoft-standard-WSL2 (root@f9c826d3017f) (gcc (GCC) 11.2.0, GNU ld (GNU Binutils) 2.37) #1 SMP Tue Nov 5 00:21:55 UTC 2024

Distro Version

Debian 12.10

Other Software

in WSL2 VM: vLLM
in host OS: Docker (using WSL2 backend)

Repro Steps

run vLLM with option --host 0.0.0.0 --port 9900.
Then connect on Windows host via:

curl "http://127.0.0.1:9900/" # won't work, refused
curl "http://192.168.1.2:9900/" # won't work, either from local PC or remote computer. 

Quick fix, in WSL 2, do:

python -m http.server --bind 0.0.0.0 9900
# it will say error: Address already in use! 

curl "http://127.0.0.1:9900/" # now works! 

Expected Behavior

A port should be open directly if bound to 0.0.0.0.

Actual Behavior

I had to use another program to bind to 0.0.0.0, see the error message, then the connection was fixed.

Diagnostic Logs

No response

Start by reproducing the WSL 2 mirrored-networking behavior with vLLM bound to 0.0.0.0 on port 9900, then compare it with python -m http.server --bind 0.0.0.0 9900. Investigate the networking path responsible for the bind and forwarding behavior; done means the documented curl requests reach a service bound to 0.0.0.0 without the workaround.