Current solutions for the specific problem of IP Multicast inter-working between IP access networks and wireless and mobile ad hoc networks are not able to work with standard IP multicast routers. We propose the MMARP protocol which is able to provide a smooth interoperation without an impairment in the overall performance. Modular routers are arousing a great interest, although some people have concerns regarding their performance. We show by comparing a C++ and a Clickbased implementation of the MMARP protocol the validity of our proposal as well as the benefits of using modular routers to easily implement ad hoc routing protocols without any reduction in the protocol's performance.