The lack of fixed infrastructure in ad hoc networks causes nodes to rely more heavily on peer nodes for communication.Nevertheless,establishing trust in such a distributed environment is very difficult, since it is not straightforward for a node to determine if its peer nodes can be trusted.An additional concern in such an environment is with whether a peer node is merely relaying a message or if it is the originator of the message.In this paper,we propose an authentication approach for protecting nodes in mobile ad hoc networks.The security requirements for protecting data link and network layers are identified and the design criteria for creating secure ad hoc networks using several authentication protocols are analyzed.Protocols based on zero knowledge and challenge response techniques are presented and their performance is evaluated through analysis and simulation. The lack of fixed infrastructure in ad hoc networks causes nodes to rely more of heavily on peer nodes for communication. Promising, such as a distributed environment is very difficult, since it is not straightforward for a node to determine if its peer nodes can be trusted. Another concern in such an environment is with whether a peer node is merely relaying a message or if it is the originator of the message. This paper, we propose an authentication approach for protecting nodes in mobile ad hoc networks. security requirements for protecting data link and network layers are identified and the design criteria for creating secure ad hoc networks using several authentication protocols are.Protocols based on zero knowledge and challenge response techniques are presented and their performance is evaluated through analysis and simulation.