The paper describes the design and implementation of MAF (multicast active fiable), a novel, fully reliable, multicast protocol that takes advantage of active network technologies. To address scalability, MAF organizes active routers into an explicit hierarchical structure that amounts to dividing the multicast tree into subtrees. Inside each subtree, MAF executes a sender initiated approach: active routers act on their immediate children as the source by storing a sender's transmissions in order to be able to retransmit them later to repair downstream losses. In order to work correctly with finite memory, MAF also requires active routers periodically to send upstream aggregated ACK messages or AACKs. AACKs result from the aggregation of the ACKs received from their immediate children in the multicast tree. By sending AACKs upstream, the routers indicate the amount of data that they are capable of storing. MAF ensures fully reliable multicast with finite memory at active routers. The paper also describes the implementation of MAF over the active network platform deployed in France by the RNRT project AMARRAGE.