Communicate some pros topics across a restricted number of ports

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I'm working on a project requiring the connectivity between multiple robots and a server to be restricted to a limited amount of predetermined ports. From my understanding, I cannot use a ROS Network as it requires access to all ports between the machines and I'm not able to obtain that. Is there a method used for transmitting a subset of topics via predefined ports?

I was looking at alternatives such as running multimaster implementations as suggested in this post, but I can't seem to find any indication that this would run on predefined ports.

Has anyone had experience with something of this kind before?
Any help is appreciated