4. Network configuration#


If you don’t have two PCs at your hand or if you are just not interested in inter-machine-communication, just skip this topic. It is not essential for the next tutorials to use cloud communication.

Of course, you can use a virtual machine (e.g. with VMWare or VirtualBox) as second PC. Just add a host-only adapter to your VM.

Quite often you want data to flow between eCAL nodes on different machines. eCAL can run in two modes, that differ from each other: local mode and cloud mode.

Local mode vs. cloud mode#

Local mode

Cloud mode

  • Uses localhost ( for registration (-> e.g. telling others about new topics and subscribing to topics)

  • Uses Multicast ( for registration

  • Uses shared memory to send actual data to other processes

  • Uses UDP multicast (239.0.0.x) to send data to other hosts

  • Uses shared memory to send data to processes on the same host

4.1. Enable network-mode in ecal.ini#


Up to eCAL 5.9, eCAL shipped with a cloud-mode-configuration by default. This changed with eCAL 5.10.

So since eCAL 5.10 you will have to enable network-mode first.

By default, eCAL is configured in local mode. To switch eCAL to cloud mode, edit your ecal.ini and change the following settings:

  • Windows: C:\ProgramData\eCAL\ecal.ini

  • Ubuntu: /etc/ecal/ecal.ini

network_enabled           = true
multicast_ttl             = 2

The multicast_ttl setting configures the time to live of the UDP datagrams, i.e. the number of hops a datagram can take before it is discarded. Usually, 2 is sufficient, but if you have a network with many routers, you may have to increase that number.

See also

Also see the advanced section to learn about changing between local mode and cloud mode!

4.2. Multicast route configuration#

Now that you have set eCAL to cloud mode, it will already start sending out UDP Multicast packages for detecting other eCAL Nodes. Your Operating System however has to send those Multicast packages to a proper network interface controller (NIC). This is not trivial, as the destination IP does not “really” exist.

Therefore you have to create a route, i.e. a 239.0.0.x -> outgoing NIC mapping.

4.2.1. Multicast configuration on Windows#

  1. Check the IPv4 address of the ethernet adapter you are using to connect your two PCs. You can do that by typing ipconfig in a command prompt. You will need the IP of your current machine you are setting the route on.

  2. Open a command prompt with administrator privileges

  3. Enter the following line and replace xx.xx.xx.xx with your IP address

    route -p add mask xx.xx.xx.xx


    If you made a mistake, you can delete your route/s with route delete Your eCAL communication may not work, if you leave faulty routes in place.

  4. Reboot

  5. Check the result from a command prompt. It should show your route under IPv4 Route Table / Persistent Routes.

    route print
    Windows route print


It is recommended to assign a static IP, so your multicast route will not become outdated at some point.

4.2.2. Multicast configuration on Ubuntu#

You can configure the multicast route in various ways, depending on your Ubuntu version.

Jump to your section of choice below:

  1. Choose how to create routes:

    • Via netplan (Recommended for Ubuntu 18 and up. Even integrates into the GUI.)

    • Via GUI (Works well for desktop Ubuntu)

    • Via /etc/network/interfaces (Legacy, up to Ubuntu 18. Not supported in Ubuntu 20, any more.)

  2. Test the configuration

Netplan is used since Ubuntu 18 and should be used in favor of the legacy (but well known) /etc/network/interfaces file. While Ubuntu 18 supports both out of the box, for Ubuntu 20 this is the only file-based networking configuration method.


Netplan uses YAML files for configuration. YAML uses spaces (' ') as indentation and does not work with tabs ('\t'). When using gedit, it is recommended to configure it to use spaces instead of tabs.

Space indentation in gedit
  1. Configure the loopback multicast route (this will become active, if you disconnect from all networks).

    sudo gedit /etc/netplan/50-ecal-multicast-loopback.yaml

    Paste the following configuration:

    # eCAL route for loopback (lo)
      version: 2
          renderer: networkd
            - to:
              metric: 1000
  2. Configure the external multicast route. This will get a lower metric and will thus become the preferred route once the interface is up.

    sudo gedit /etc/netplan/50-ecal-multicast.yaml

    Paste the following configuration and replace eth0 with your desired interface:

    # Replace eth0 with your network adapter!
      version: 2
      renderer: NetworkManager # GUI integration for desktop Ubuntu
        # Replace eth0 with your interface!
          # Either use DHCP...
          dhcp4: yes
          dhcp6: yes
          # ... or configure a static address!
          #  -
            - to:
              metric: 1
  3. Apply the changes

    sudo netplan apply


    In Ubuntu 20.04 and up you may also have to activate the netplan setting in the network configuration GUI!

    Activate the netplan settings from the Gnome GUI Test the configuration#

Check the result from a terminal. It should show routes for local and external communication:

route -n
Ubuntu route -n

4.3. eCAL Samples over network#

Now start one ecal_sample_person_snd and one ecal_sample_person_rec, just as in the previous section. But on different machines! If you configured everything correctly, publisher and subscriber should connect almost immediately and exchange data.

person_snd and person_rec sample over network