DDS communication between Windows and container running in WSL

[tim-schaechterle]

Hello everybody,

I am working with a system consisting of four processes that communicate with each other via DDS. Their runtime environments are mixed between WSL containers and the Windows host:

• machine: C++, running in a container on WSL
• settings: C++, running in a container on WSL
• testscripts: Python, running in a container on WSL
• ads2dds: C++, running natively on the Windows host

All processes use the same profiles.xml, which contains our Fast DDS participant configuration.
The three WSL‑based components run inside a single Podman pod with hostNetwork: true.
Until recently, all DDS participants were able to discover each other and communicate normally.
However, since about one week ago, discovery and communication between the Windows host and the WSL containers stopped working, even though:

• nothing changed in the profiles.xml
• the containers still run in the same pod with hostNetwork: true
• the WSL system is configured to use network mirroring
• the WSL‑internal DDS participants (machine, settings, testscripts) can still discover each other

The Windows‑based process (ads2dds) now either:

• does not discover the WSL participants at all, or
• discovers only participant info, but no data is received or transmitted

This strongly suggests that WSL ↔ Windows loopback mirroring (particularly for UDP packets) is no longer functioning the way it used to. My goal now is to understand the cause and find a reliable solution — potentially using a DDS Router — and to clarify whether our existing profiles.xml is still required.

Regards
Tim

---

my pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: systemtest
spec:
  hostNetwork: true
  restartPolicy: OnFailure
  containers:
    - name: settings
      image: registry.gitlab.xxx.de/settings:latest
      volumeMounts:
        - name: fastdds-profiles
          mountPath: /etc/fastdds
      env:
        - name: FASTDDS_DEFAULT_PROFILES_FILE
          value: /etc/fastdds/profiles.xml

    - name: machine
      image: registry.gitlab.xxx.de/machine:latest
      volumeMounts:
        - name: fastdds-profiles
          mountPath: /etc/fastdds
      env:
        - name: FASTDDS_DEFAULT_PROFILES_FILE
          value: /etc/fastdds/profiles.xml

    - name: testscript
      image: registry.gitlab.xxx.de/testscripts:latest
      volumeMounts:
        - name: fastdds-profiles
          mountPath: /etc/fastdds
      env:
        - name: FASTDDS_DEFAULT_PROFILES_FILE
          value: /etc/fastdds/profiles.xml

  volumes:
    - name: fastdds-profiles
      hostPath:
        path: src/
        type: Directory

---

my profiles.xml

<?xml version="1.0" encoding="UTF-8"?>
<profiles xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
  <participant profile_name="DS_CLIENT" is_default_profile="true">
    <rtps>

      <defaultUnicastLocatorList>
        <locator>
          <udpv4>
            <address>127.0.0.1</address>
          </udpv4>
        </locator>
      </defaultUnicastLocatorList>

      <builtin>

        <avoid_builtin_multicast>false</avoid_builtin_multicast>

        <metatrafficMulticastLocatorList>
          <locator>
            <udpv4>
              <address>239.255.0.1</address>
            </udpv4>
          </locator>
        </metatrafficMulticastLocatorList>

        <metatrafficUnicastLocatorList>
          <locator>
            <udpv4>
              <address>127.0.0.1</address>
            </udpv4>
          </locator>
        </metatrafficUnicastLocatorList>

        <initialPeersList>
          <locator>
            <udpv4>
              <address>127.0.0.1</address>
            </udpv4>
          </locator>
        </initialPeersList>

      </builtin>

    </rtps>
  </participant>

</profiles>

[tim-schaechterle]

System information:

• Windows 11 Enterprise (Build 22631.6495)
• WSL version: 2.6.3.0
• WSL distribution: Ubuntu-24.04
• FastDDS 3.2