Skip to main content

11-ROS 2 Distributed Communication (Part 2: Domain & DDS Rules)

1. Distributed Network Grouping (Domain Isolation)​

If multiple robots exist on the same network, you can prevent interference by assigning different domain IDs.

Only devices with the same ROS_DOMAIN_ID can communicate.

Add the following line to the .bashrc file on both machines:

export ROS_DOMAIN_ID=<your_domain_id>

If the host and client use different values, they will be isolated and unable to communicate.

2. Example: Domain-Based Grouping​

Host Machine​

echo "export ROS_DOMAIN_ID=6" >> ~/.bashrc
source ~/.bashrc
ros2 run demo_nodes_py talker

Slave Machine​

echo "export ROS_DOMAIN_ID=6" >> ~/.bashrc
source ~/.bashrc
ros2 run demo_nodes_py listener

If the listener receives data correctly, grouped multi-machine communication is successful.

3. ROS_DOMAIN_ID Notes​

The ROS_DOMAIN_ID value is not arbitrary. The following constraints apply:

  1. Recommended range: [0, 101]
  2. Maximum number of nodes per domain: ≤ 120
  3. For domain ID 101, the maximum number of nodes is 54

4. DDS Domain ID Calculation Rules (Advanced)​

  1. DDS communicates using TCP/IP or UDP/IP, which use port numbers:
0 – 65535
  1. DDS uses port 7400 as the starting port, and each domain occupies 250 ports by default:
(65535 - 7400) / 250 = 232 domain IDs → [0 – 231]
  1. Operating systems reserve some ports:
  • Linux: [0--101] and [215--231]
  • Windows / macOS: [0--166]

For cross-platform compatibility, [0--101] is the safest range.

5. Node Capacity per Domain​

Each ROS 2 node requires 2 ports. The first few ports are reserved for discovery.

(250 - 10) / 2 = 120 nodes

Special case:

  • For ROS_DOMAIN_ID = 101, half of the ports are reserved, reducing the max to 54 nodes.

These rules are important for large-scale robotic systems and multi-robot network planning.