[Zope] multi zope communication

I am interested in two or more zopes talking to each other, particularly to lookup data and display results on the other or to send data from one to the other - so client and server. Not simple syndication from one to the other but real two way communication. I am thinking of using XML RPC because I am not sure on whether SOAP can work properly on zope from basic material I have read thus far. What is most practical for production sites? Anyone have experience using zope as a client and server in this way? I am also particularly interested in any recommendations for handling authentication and encryption in such a case. Regards, David