Packet delay and bandwidth are two important metrics for measuring quality of service (QoS) of Internet services. While proportional delay differentiation (PDD) has been studied intensively in the context of differentiated services, few studies were conducted for per-class bandwidth differentiation. In this paper, we design and evaluate an efficient bandwidth differentiation approach. The DIBS (dual interval bandwidth scheduling) approach focuses on the short-term bandwidth differentiation of multiple classes because many Internet transactions take place in a small time frame. It does so based on the normalized instantaneous bandwidth, measured by the use of packet size and packet delay. It also proposes to use a look-back interval and a look-ahead interval to trade off differentiation accuracy and scheduling overhead. We implemented DIBS in the click modular software router. Extensive experiments have demonstrated its feasibility and effectiveness in achieving short-term bandwidth differentiation. Compared with the representative PDD algorithm WTP, DIBS can achieve better bandwidth differentiation when the inter-class packet size distributions are different. Compared with the representative weighted fair queueing algorithm PGPS, DIBS can achieve more accurate or comparable bandwidth differentiation at various workload situations, with better delay differentiation and lower cost.