Considerable efforts have focused on congestion control protocols for large-scale multicast applications, but in most cases, these consider only single rate sessions. In heterogeneous environments, it is interesting to offer each receiver its maximum fair rate, regardless of the presence of slower receivers in the group. In this paper, we propose an alternative to layered encoding/transmission schemes. TUF, our Tag-based UDP multicast Flow control protocol, uses very simple router filters, that, as RED or diffserv, are not aware of the transport layer, do not add flow state, nor intensive computation. Filtering is done based on packet «tags», computed at the source, and provides fair bandwidth sharing. We believe that this scheme can coexist with TCP, and can also be useful for reliable multicast applications.