Communication apparatus includes a plurality of interfaces for receiving and transmitting data packets from and to a network and a memory, which receives and stores context data with respect to multicast groups. Packet processing circuitry establishes reliable connections over the network with the receiving nodes in the multicast groups, and upon receiving from a packet source on the network an incoming unicast packet containing multicast data and containing multicast metadata that identifies a multicast group, sends an acknowledgment of the incoming unicast packet to the packet source, reads the context data from the memory with respect to the identified multicast group, and transmits multiple outgoing unicast packets containing the multicast data via respective egress interfaces to the receiving nodes in the multicast group over the reliable connections.