The genI3MiddleBoxConf program in i3/i3OCD directory takes as input the name to be given to S and M, and produces the XML snippets that you need to paste into the myNames.xml configuration files corresponding to S and M. In the proxy-config.xml corresponding to M, you need to set [functionAsMiddleBox] to yes. You also need to set [middleBoxType] to bro or the type of your specific middlebox. It is always easier to start with the example configuration files in the demos subdirectory. There is a detailed README file in the demos directory that gives step by step instructions for starting up OCALA and bro.