This paper proposes a congestion avoidance mechanism that addresses unicast (TCP or UDP) as well as multicast (UDP) best effort flows. Our mechanism originally combine explicit congestion notification (ECN) based on router active queue management to detect congestion, with ICMP source quench messages to inform the involved sources of the network congestion state. The fairness achieved is a trade-off between TCP-like and max-min fairness. We demonstrate through simulation that the proposed mechanism enforces fairness and provides an efficient and simple solution to congestion avoidance.