For more than a decade, IP over Ethernet has been the dominating local area network technology because it is cost-efficient, simple and reliable. Unfortunately, it does not support the transport of continuous data as generated by multimedia applications. The large number of IP installations makes it necessary to find ways to provide support for multimedia applications in existing network environments without making interfaces used by existing applications incompatible. In this paper, we present the design, implementation and evaluation of the Network Resource Allocation Protocol NetRAP. NetRAP extends IP in that it allows applications to allocate bandwidth. Access to the network happens in two phases. In the first phase, a token-based access protocol is used to give applications with bandwidth reservations access to the network. In the second phase, the network is operated in normal CSMA/CD mode giving all other applications without bandwidth reservations the opportunity to access the network. For this purpose, we have extended an existing IP stack with a transport protocol able to control access times. Our performance measurements show that NetRAP adds little overhead. Since the implementation of NetRAP only requires few modifications of existing protocol software and, moreover, does not invalidate existing networked applications, it offers a simple and cost-efficient alternative to other more complex solutions.