The main issue I'm seeing with your code is that your TCP port is incorrect. The RT Box listens to XML-RPC connections on TCP port 9998. I made a few small fixes to your code. The following code should work.
ip = socket.gethostbyname('rtbox-20b0f703a3f4.local.')
server=xmlrpclib.Server("http://" + ip + ":9998/RPC2")
with open("C:Models/boost_converter_codegen/Plant.elf", "rb") as f:
print("Real-time simulation running")
Also, have you checked out the XML Scripting demo model? If you haven't yet, I recommend you to do so. It is under Window > Demo Models > RT Box Demo Models > XML-RPC Scripting Interface. This demo model is pretty good at explaining this feature step by step, using a simple example.