ROS 2 Interop

nano-ros communicates with standard ROS 2 nodes using the rmw_zenoh_cpp middleware. Both sides connect to the same zenohd router and exchange CDR-encoded messages with compatible key expressions.

Prerequisites

• ROS 2 Humble installed
• rmw_zenoh_cpp package (sudo apt install ros-humble-rmw-zenoh-cpp on Ubuntu, or build from source)
• zenohd router running

Quick Start

Open three terminals:

# Terminal 1: Start the zenoh router
zenohd --listen tcp/127.0.0.1:7447

# Terminal 2: Run the nano-ros talker
cd examples/native/rust/talker
RUST_LOG=info cargo run

# Terminal 3: Run a ROS 2 listener
source /opt/ros/humble/setup.bash
export RMW_IMPLEMENTATION=rmw_zenoh_cpp
export ZENOH_CONFIG_OVERRIDE='mode="client";connect/endpoints=["tcp/127.0.0.1:7447"]'
ros2 topic echo /chatter std_msgs/msg/Int32 --qos-reliability best_effort

You should see the ROS 2 listener printing messages published by nano-ros:

data: 1
---
data: 2
---

The Other Direction

ROS 2 publishers also work with nano-ros subscribers:

# Terminal 2: Run the nano-ros listener instead
cd examples/native/rust/listener
RUST_LOG=info cargo run

# Terminal 3: ROS 2 talker
source /opt/ros/humble/setup.bash
export RMW_IMPLEMENTATION=rmw_zenoh_cpp
export ZENOH_CONFIG_OVERRIDE='mode="client";connect/endpoints=["tcp/127.0.0.1:7447"]'
ros2 topic pub /chatter std_msgs/msg/Int32 "{data: 42}" --qos-reliability best_effort

Discovery

nano-ros publishes ROS 2-compatible liveliness tokens, so standard ROS 2 tools work:

source /opt/ros/humble/setup.bash
export RMW_IMPLEMENTATION=rmw_zenoh_cpp
export ZENOH_CONFIG_OVERRIDE='mode="client";connect/endpoints=["tcp/127.0.0.1:7447"]'

ros2 topic list        # Shows /chatter
ros2 topic info /chatter   # Shows publisher/subscriber count
ros2 node list         # Shows nano-ros nodes

Configuration

Domain ID

Both sides must use the same ROS domain ID. nano-ros reads ROS_DOMAIN_ID from the environment (default: 0):

ROS_DOMAIN_ID=42 cargo run    # nano-ros side
ROS_DOMAIN_ID=42 ros2 topic echo /chatter ...  # ROS 2 side

QoS

nano-ros defaults to BEST_EFFORT reliability and VOLATILE durability. When using ROS 2 subscribers, match the QoS:

ros2 topic echo /chatter std_msgs/msg/Int32 --qos-reliability best_effort

Without --qos-reliability best_effort, ROS 2 defaults to RELIABLE, which won’t match the nano-ros publisher’s BEST_EFFORT QoS.

rmw_zenoh Client Mode

By default, rmw_zenoh_cpp uses peer mode and won’t connect to a zenohd router. Force client mode with:

export ZENOH_CONFIG_OVERRIDE='mode="client";connect/endpoints=["tcp/127.0.0.1:7447"]'

Set this before any ros2 command.

Protocol Details

nano-ros uses the same wire format as rmw_zenoh_cpp:

• Data key expression: <domain_id>/<topic>/<type>/TypeHashNotSupported (Humble). Example: 0/chatter/std_msgs::msg::dds_::Int32_/TypeHashNotSupported
• Liveliness tokens: @ros2_lv/<domain>/<zid>/0/... for discovery
• Message encoding: CDR little-endian with 4-byte encapsulation header [0x00, 0x01, 0x00, 0x00]
• RMW attachment: 33-byte metadata (sequence number, timestamp, GID) appended via Zenoh attachment

ROS 2 Iron and Beyond

Iron uses actual type hashes (RIHS01_<sha256>) instead of TypeHashNotSupported. nano-ros currently supports Humble only. Iron support is planned.

Troubleshooting

Topic not visible in ros2 topic list: Ensure both nano-ros and ROS 2 use the same domain ID and that rmw_zenoh_cpp is in client mode pointing to the same router.

Discovery works but no messages received: Check that the QoS matches. Use --qos-reliability best_effort on the ROS 2 side.

rmw_zenoh not connecting: Verify ZENOH_CONFIG_OVERRIDE is set. Without it, rmw_zenoh uses peer mode and won’t find the router.

Next Steps

• Architecture — understand the layer model
• RMW Zenoh Protocol — full wire format reference