We consider the problem of multicast routing in a large single domain network with a very large number of multicast groups with small number of receivers. Such a case occurs, for example, when multicast addresses are statically allocated to mobile hosts, as a mechanism to manage Internet host mobility. For such networks, existing dense or sparse mode multicast routing algorithms do not scale well with the number of multicast groups. We introduce an alternative solution called Distributed Core Multicast (DCM). DCM is based on an extension of the centre-based tree approach. It uses several core routers, called Distributed Core Routers (DCRs) and a special control protocol among them. The objectives are: (1) to avoid multicast group state information in backbone routers, (2) to avoid triangular routing across expensive backbone links, (3) to scale well with the number of multicast groups. We describe how our approach can be used to support mobile hosts. We argue that, when DCM is used to route packets to mobile hosts, good performance can be achieved during handoffs.