[ROS2] Finding the originating socket for a ROS2 node

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I have created my own little node called tester_publisht, and am trying to find the originating socket of the node. However, the node is using 4 separate ports, and I have no idea what the output means.

user@ubuntu:~$ lsof -iUDP
COMMAND     PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
spotify    2067 user   92u  IPv4 276438      0t0  UDP *:57621 
spotify    2067 user  108u  IPv4 276451      0t0  UDP *:1900 
spotify    2067 user  128u  IPv4 276452      0t0  UDP *:55193 
tester_pu  9642 user    6u  IPv4 241204      0t0  UDP *:7400 
tester_pu  9642 user    7u  IPv4 241207      0t0  UDP *:7412 
tester_pu  9642 user    8u  IPv4 241210      0t0  UDP *:7413 
tester_pu  9642 user    9u  IPv4 241213      0t0  UDP *:41004 
rqt_graph 14766 user   24u  IPv4 243242      0t0  UDP *:7400 
rqt_graph 14766 user   25u  IPv4 243246      0t0  UDP *:7414 
rqt_graph 14766 user   26u  IPv4 243250      0t0  UDP *:7415 
rqt_graph 14766 user   27u  IPv4 243253      0t0  UDP *:39130 
_ros2_dae 19978 user    6u  IPv4 250922      0t0  UDP *:7400 
_ros2_dae 19978 user    7u  IPv4 250927      0t0  UDP *:7416 
_ros2_dae 19978 user    8u  IPv4 250932      0t0  UDP *:7417 
_ros2_dae 19978 user    9u  IPv4 250935      0t0  UDP *:36155

tester_publisht, rqt_graph and _ros2_daemon are the nodes that are running (sorry about Spotify :) ).

Running ros2 node list -a reveals the three nodes above, and running ros2 topic list returns /clock (the topic that tester_publisht is publishing to), /parameter_events and /rosout.

I tried to listen in on the ports for tester_publisht, but was only able to listen onto port 7400. The rest (7412, 7413, and 41004) could not be listened to:

user@ubuntu:~$ nc -lvu 7400
Listening on [0.0.0.0] (family 0, port 7400)
Connection from ubuntu 39130 received!
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     brqt_gui_py_node_14766,,(name=rqt_gui_py_node_14766;namespace=/;
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user@ubuntu:~$ nc -lvu 7412
nc: Address already in use
user@ubuntu:~$ nc -lvu 7413
nc: Address already in use
user@ubuntu:~$ nc -lvu 41004
nc: Address already in use

However, port 7400 is also shared with the other two nodes rqt_graph and _ros2_daemon, as shown in the first code block.

So I don't really understand what is the significance of port 7400. And also, which is the originating socket for tester_publisht, or for each of the nodes for that matter?