ROS2-foxy nodes can't communicate through docker container border

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I'm new to ROS2. I've got a somewhat weird setup that I'm trying to launch. My issue is that minimal publisher and subscriber from examples don't hear each other.

I've got a docker container, based on Ubuntu 18.04, with ROS2 Foxy installed from sources. This container has installed environment that I have to use, namely, CUDA 10.0 and some software using it.

This container is run on Ubuntu 20.04 host. This host has also installed ROS2 Foxy from Debian packages.

I run the container with --net host, then launch minimal subscriber from examples in it. Then I run minimal publisher on the host.

That is on host:

$ docker run --rm -it --net host container

In container:

# ros2 run examples_rclpy_minimal_subscriber subscriber_member_function

On host in another terminal:

$ source /opt/ros/foxy/setup.zsh
$ ros2 run examples_rclpy_minimal_publisher publisher_local_function

The issue is that the subscriber doesn't hear anything from the publisher. The same issue is observed, if I swap subscriber and publisher, that is run publisher in the container and subscriber on the host.

If I execute both subscriber and publisher in the container, subscriber hears it. On host:

docker exec -it container /bin/bash

In container:

ros2 run examples_rclpy_minimal_publisher publisher_local_function

And subscriber prints "I heard hello".

At the same time, multicast messages (ros2 multicast send, ros2 multicast receive) are sent and received successfully.

If I run the container without --net key, then the subscriber running in it, sees messages from the publisher. However, this limits usage of the container. It won't be seen from another PC.

I've pasted the minimal Dockerfile illustrating the issue at the bottom of this message (unfortunately, I cannot attach it).

I've also pushed image to the dockerhub, and it can be downloaded with the command docker pull wl2776/nvidia-ros:latest

What I've also checked.

1. Running netcat both in container and on host shows that the traffic is passed through the container boundary. If I replace subsriber in the container with netcat it prints several packets. That is, on host:

   $ docker run --rm -it --net host container
   $ docker cp /bin/nc.openbsd container:/tmp
   

   In container:

   # /tmp/nc.openbsd -l -u -p 7400 | od -
   

   On host in another terminal:

   $ source /opt/ros/foxy/setup.zsh
   $ ros2 run examples_rclpy_minimal_publisher publisher_local_function
   

   And I see several dumps from nc

2. I've also tried the experiment with minimal publisher and subscriber using docker image tagged osrf/ros:foxy-desktop from dockerhub. Everything has worked perfectly.

3. When minimal subscriber runs in the container, its node and topic are seen on the host. On host, while subscriber in the container is running:

   $ ros2 topic list
   /parameter_events
   /rosout
   /topic
   $ ros2 node list
   /minimal_subscriber
   

   If I stop minimal subsriber in the container with Ctrl-C, then it disappears from ros2 node list

4. Sniffing packets with tcpdump shows that subscriber in OSRF's container sends RTPS packets with version 2.3, but mine - with version 2.2. They also have different sizes (252 bytes from OSRF's ...