1. A method comprising: receiving a request for content, at a requestor having one or more processors, from a first receiver; initiating a quality of service aware hybrid tree construction by sending a multicast service level specification message to a first overlay tree manager, the multicast service level specification message specifying a source, one or more receivers and a quality of service (QoS) guarantee required; electing an overlay tree manager at the source as initiator of overlay tree construction; computing, at the initiator of overlay tree construction, an overlay tree; dividing, at the one or more processors, the overlay tree at the initiator of overlay tree construction and communicating with other overlay tree managers in the network; computing, at each overlay tree manager, a shortest path tree using a constrained algorithm; sending, from each overlay tree manager, a multicast service level specification message to each Internet protocol (IP) manager in the network requesting that each IP manager construct an IP multicast tree for an IP island corresponding to that IP manager, where each node in the IP multicast tree corresponds to a physical router in the IP island and install the IP multicast tree on one or more corresponding physical routers in the IP island; and enforcing multicast routes and quality of service on the one or more routers.