not getting udp multicast working in the new mirrored network mode of WSL2, how to?

[LuukBerkel]

According to the release information multicast should be supported in the new mirrored network mode of wsl2. Only when i try to use it i can only send multicast udp frames but i cannot receive them. Is this an issues with the windows firewall or does anyone else know, i have not enabled the new firewall option though?

This because i am trying to run ros2 in wsl2. And when i run ros2 multicast receive in wsl2 i am not able to receive any messages from an host on my local network. I and i am sure it is reachable because i can ping it and ssh into it. So when i run ros multicast send on a host on the same network, the ros2 multicast receive in my wsl2 should print hello world, but it doesn't. It does work the other way around though.

Did anyone else get this working, else i will open an issue in the issues queue? I have also use sockperf to test but it also doesn't work, although i may have done it wrong.

##Build:

• WSL-versie: 2.0.4.0
• Kernelversie: 5.15.123.1-1
• Windowsversie: 22H2 on preview channel

[checkraisefold]

Can repo, WSL 2.0.4.0 with same of rest of version info.

[sacefe]

I have same problem described by Luuk using the latest prerelease 2.0.6 :(

[guitarpicva]

Same in WSL v 2.0.9

[checkraisefold]

Currently I was able to get multicast (through lan 255 address at least) working by turning on hostAddressLoopback. If it doesn't work, which sometimes it does break, rebooting my PC entirely (not restarting WSL) seemed to fix it. Could work for some people.

[sacefe]

Hi, could you please explain more about the 255 address?

[kistlin]

For me it worked after adding a firewall exception. The rule was an Inbound rule to allow a certain UDP port range.

Except I have
[wsl2]
firewall=true

WSL version: 2.0.7.0
Kernel version: 5.15.133.1-1
WSLg version: 1.0.59
Windows version: 10.0.22631.2506

So maybe it's something with the firewall not working yet?

[ben-xD]

Wouldn't turning on firewall for WSL traffic make things worse? I just noticed this value is on by default, so i'll try turn it off.

[borjamunozf]

I think multicast does not work with mirrored mode.

• Tested with CONFIG_IP_MULTICAST=y kernel config enabled but same result.
• Tested with 2.1.15, 2.2.24 and 2.3.31
  Applied multiple changes and rules in HyperV and Windows Firewall without success.
  Tested with this example Applications running on host not receiving UDP multicast packets sent from WSL2 #12122 and the only way to make it work was setting up Bridged mode and external VMswitch.

My guess right now is that the internal VMSwitch that WSL uses by default does not allow multicast traffic or it's not able to forward properly (ex: hyperv multicast routing iss

Also it works with WSL distro version 1

If anyone is able to make the example I mentioned with Mirrored mode, please, let me know

[ben-xD]

A relevant issue: #10735

I ran wireshark inside WSL, and I can see multicast traffic being received. I run wireshark with sudo wireshark inside WSL though.