PyPi server firewall and ports options

I am running devpi-server on the host to host some python packages. On my laptop, I can download them with pip install --index <hostname>

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On another host though, the same thing works showing me a package not found error. It looks like it doesn't find the package on the devpi-server node and falls back to the global PyPi server.

I think it is a firewall or port issue. What firewall / ACL access permissions do I need for the host to see my PyPi server hosted on the devpi server? devpi-server is running on port 4040, so I open port 4040.

I tried to put a ticket to the devpi-server project, but I've been going back and forth with the maintainer for a week and he doesn't seem to understand what the question is, so I hope someone here can help me.

Any ideas?

EDIT : Using devpi-client I can install the packages correctly. What's different from installing pip --index? Do you need any specific ports to open or specific permissions?