Transports: Zenoh vs DDS

Conduit publishes ROS 2 messages over one of two transports. This page helps you pick one and set it up.

The easiest way to set up either one is Connect with a QR code (Conduit 2.6.0 or later): a script on your ROS 2 PC checks the setup, and scanning its QR code fills in the connection settings in Conduit.

Quick decision

Your ROS 2 setup	Transport
Uses `rmw_zenoh_cpp`	Zenoh
Uses `rmw_cyclonedds_cpp`	DDS
Device and host on different subnets, or over the internet	Zenoh (for example over Tailscale)
Same LAN, and you don't want to run a router	DDS
Network blocks multicast or isolates Wi-Fi clients	Zenoh (TCP)

The default RMW on Humble, Jazzy, Kilted, Lyrical and Rolling is Fast DDS (rmw_fastrtps_cpp), so set RMW_IMPLEMENTATION on the host. A Fast DDS host can discover Conduit over DDS, but may drop or delay high-rate topics such as the camera and LiDAR.

Side by side

	Zenoh	DDS (CycloneDDS)
ROS 2 RMW	`rmw_zenoh_cpp`	`rmw_cyclonedds_cpp`
Router required	Yes (`rmw_zenohd`)	No
Discovery	Through the router	Multicast; add peers for unicast on top (hybrid)
Network traffic	TCP, port 7447 by default	UDP, from `7400 + 250 × domain ID`
Across subnets	Yes	No (same LAN only)
Tailscale	Yes	No
Network interface on iPhone / iPad	Any that reaches the router	en0 (WiFi)
Domain ID	0–232	0–232
Large messages (camera, LiDAR)	TCP to the router	UDP fragments; busy Wi-Fi may drop them

Conduit embeds CycloneDDS 11.0.1. Use the rmw_cyclonedds_cpp that ships with your ROS 2 distribution.

Settings

Open Settings (gear icon) in Conduit. Changes are saved as you make them; tap Done to close. You cannot change the connection while publishing.

Zenoh:

Transport: Zenoh
Router Address: the IP address of the host that runs rmw_zenohd
Router Port: 7447
Domain ID: the host's ROS_DOMAIN_ID
Distribution: your host's ROS 2 release (Lyrical by default)

Start the router on the host:

export RMW_IMPLEMENTATION=rmw_zenoh_cpp
ros2 run rmw_zenoh_cpp rmw_zenohd

DDS:

Transport: DDS
Discovery: opens the DDS Discovery page:
- Peers: add the ROS 2 host's IP address. With no peers, Conduit uses multicast discovery. With peers, it also sends unicast discovery to them (hybrid).
- Network Interface: en0 (WiFi) on iPhone and iPad.
- This Device shows the device's IP address.
Domain ID: the host's ROS_DOMAIN_ID
Distribution: your host's ROS 2 release (Lyrical by default)

Discovery changes apply the next time you tap Start.

On the host, add the device's address (This Device) as a peer too:

export RMW_IMPLEMENTATION=rmw_cyclonedds_cpp
export CYCLONEDDS_URI='<CycloneDDS><Domain><Discovery><Peers><Peer address="DEVICE_IP"/></Peers></Discovery></Domain></CycloneDDS>'
ros2 daemon stop

Replace DEVICE_IP with the address shown under This Device. Run ros2 daemon stop after you change RMW_IMPLEMENTATION, ROS_DOMAIN_ID or CYCLONEDDS_URI, so the ros2 CLI picks up the change.

Network requirements

Zenoh: the device must reach the router over TCP (port 7447 by default). Allow that port in the host's firewall.
DDS: the device and the host must be on the same LAN subnet, with UDP allowed on the DDS ports: 7400 + 250 × domain ID and the next 249 ports. Guest and office Wi-Fi often isolate clients from each other ("AP isolation"), which blocks DDS. Use Zenoh on such networks, or disable AP isolation.

Tailscale

Zenoh works over a Tailscale tailnet, so the device and the host can be on different networks. Put both on the same tailnet and use the host's Tailscale address as the Router Address. The QR code script sets this up with --tailscale; see Connect with a QR code. DDS does not work over Tailscale.

When to switch

Use Zenoh if:

Large camera or LiDAR messages drop on DDS.
You need to connect from another subnet or from outside the LAN.
Your Wi-Fi blocks multicast or isolates clients, and you cannot change it.

Use DDS if:

Your ROS 2 nodes already use CycloneDDS and you don't want to run a Zenoh router.
You want the shortest network path, with no hop through a router.