Abstract: Numerous works have complained the sensitivity to network load and instability of Random Early Detection (RED), an active queue management (AQM) scheme, under various network configurations. In this work, we focus on our investigation on the stability of the active queue management (AQM) in routers. By modeling the close-looped congestion control systems in a differential fluid flow model, we reach the sufficient and necessary condition to stabilize the dynamical system. By exploring the convergence region and root-locus of the system and studying the parameter effects of RED in various network simulation conditions, we show the limits of RED in nature and argument against deploying RED in high-speed switches.