Despite huge research available on MANET, a lot is yet to be done, particularly the development of routing protocols optimized for specific applications. Since infancy, MANETs were optimized for applications where group management is strict. However, with the advent of VANETs and local area social networks as offering of MANETs to common people (we call open-MANETs), there is a need to revise routing protocols to allow for this open-ness. In this paper we draw our attention to multicast routing protocol for applications where group management is not an essential aspect to deal with. A brief survey of existing multicast routing protocols including MAODV and PUMA is accompanied by a discussion regarding the evolution of SLIM+ protocol; that is specifically targeted for such open-MANETs. In this paper we also compare these three multicast routing protocols with respect to their robustness.