A mechanism is provided by which a transport tree identifier can be generated comprising both an opaque field, containing information that cannot be interpreted by core routers, and a non-opaque field, containing information that can be interpreted by core routers. The transport tree identifier is then used in the process of building a transport tree across a transport network. A transport network egress router can receive a request to join a multicast datastream from a downstream node outside of the transport network. The information contained in the join message that identifies the desired multicast datastream is encoded in the opaque field of the transport tree identifier. Information related to desired route properties is encoded in the non-opaque field, for interpretation by the core routers. The non-opaque field can also include an identifier of a root node core router for the transport tree. Route properties can be provided, for example, by selection and transmission from the customer itself, or route properties can be associated with a particular customer or associated with a port of an egress router coupled to the customer network.