Networking

ROS2 uses DDS for message transport.

Set the environment variable RMW_IMPLEMENTATION to select a DDS implementation (RMW = robotic middleware). For instance:

export RMW_IMPLEMENTATION=rmw_cyclonedds_cpp

To check which RMW implementation is being used:

ros2 doctor --report | grep middleware

DDS Discovery

There is no rosmaster like in ROS1. Node discovery is peer-to-peer with nodes announcing their topics on startup and periodically after that. By default, any machines on the same network will see each other if they have the same ROS_DOMAIN_ID.

ROS_DOMAIN_ID can be any number between 0 and 253, although it is recommended to use numbers less than 128.

In addition to the ROS_DOMAIN_ID, CycloneDDS supports a domain tag, which allows nearly infinite partitioning of the network (see below).

If you want to limit communication to the localhost set ROS_LOCALHOST_ONLY, which is available since Eloquent.

CycloneDDS

Cyclone can be configured with XML. This can be stored in a file or passed directly in the environment variable CYCLONEDDS_URI. A full list of supported options can be found in the eclipse-cyclonedds repo. See also the Guide to Configuration.

CycloneDDS: Multiple Interfaces

Cyclone currently only works with a single network interface. If you have multiple interfaces, specify which one to use in the NetworkInterfaceAddress:

<CycloneDDS>
  <Domain>
    <General>
      <NetworkInterfaceAddress>wlp2s0</NetworkInterfaceAddress>
    </General>
  </Domain>
</CycloneDDS>

CycloneDDS: Disabling Multicast (Except Discovery)

Some network hardware can perform poorly with multicast (especially with WIFI). You can limit multicast to just discovery:

<CycloneDDS>
  <Domain>
    <General>
      <AllowMulticast>spdp</AllowMulticast>
    </General>
  </Domain>
</CycloneDDS>

CycloneDDS: Domain Tag

CycloneDDS also defines a "Domain Tag" which allows to drastically partition the network with a custom string:

<CycloneDDS>
  <Domain>
    <Discovery>
      <Tag>my_robot_name</Tag>
    </Discovery>
  </Domain>
</CycloneDDS>

Example

The above tags can all be combined:

<CycloneDDS>
  <Domain>
    <General>
      <!-- Explicitly set network interface -->
      <NetworkInterfaceAddress>wlp2s0</NetworkInterfaceAddress>
      <!-- Use multicast for discovery only -->
      <AllowMulticast>spdp</AllowMulticast>
    </General>
    <Discovery>
      <!-- This tag has to be the same on each machine -->
      <Tag>my_robot_name</Tag>
    </Discovery>
  </Domain>
</CycloneDDS>

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