Mobile ad hoc networks (MANETs) are a collection of wireless hosts that can be rapidly deployed as a multi-hop packet radio network without the aid of any established infrastructure or centralized administration. The routing security is a critical problem for MANETs. However, existing protocols are not sufficient for security requirements. In this paper, we analyze the weakness of some existing popular protocols. Then, a secure routing protocol SDSR is implemented based on end-to-end integrity check and hop-by-hop discovery request authentication. Unlike traditional technique, our neighbor monitor scheme does not work in promiscuous mode and we demonstrate that the existing overhearing scheme can not perform effectively without the support of authentication. Security and performance evaluation indicate that our scheme achieves a good security at the cost of acceptable overhead.