ros2 nodes on different subnets

edit

The problem is that fastRTPS unicast discovery based on initial peers only probes for 4 participants by default. This means that when you have more than 3 ros nodes things will fail with the above XML (roslaunch is also a node, so 4 nodes + roslaunch = 5 nodes).

The following XML solves the problem for me.

<?xml version="1.0" encoding="UTF-8" ?>

<profiles>
    <transport_descriptors>
        <transport_descriptor>
            <transport_id>veelpeers</transport_id> <!-- string -->
            <type>UDPv4</type> <!-- string -->
            <maxInitialPeersRange>100</maxInitialPeersRange> <!-- uint32 -->
        </transport_descriptor>
    </transport_descriptors>
    <participant profile_name="participant_somename" is_default_profile="true">
        <rtps>
            <builtin>
                <metatrafficUnicastLocatorList> 
                    <locator/> 
                </metatrafficUnicastLocatorList> 
                <domainId>4</domainId>
                <initialPeersList>
                    <locator>
                        <udpv4>
                                <address>192.168.1.40</address>
                        </udpv4>
                    </locator>
                    <locator>
                        <udpv4>
                                <address>192.168.2.22</address>
                        </udpv4>
                    </locator>
                    <locator>
                        <udpv4>
                                <address>127.0.0.1</address>
                        </udpv4>
                    </locator>
                </initialPeersList>
            </builtin>
            <userTransports>
            <transport_id>veelpeers</transport_id>
            </userTransports>
            <useBuiltinTransports>false</useBuiltinTransports>
        </rtps>
    </participant>
</profiles>

Note that unicast discovery sends a packet to every known port to check if there is a participant running there. so this can create a lot of network traffic.