Wireless infrastructure network is vulnerable to Denial of Service (DoS) attack which makes the resources unavailable for its intended user. As an outcome of DoS attack, authenticated user is denied from accessing the network by spoofing legitimate client identity. Reduced protection in management frame led to MAC spoof DoS attack. Though 802.11w was developed to protect the management frame, the network is vulnerable to different DoS attacks and unable to prevent all types of DoS attacks. This motivated them to propose a mechanism to detect and prevent substantial number of DoS attacks. This paper proposes an algorithm called Alternative Numbering Mechanism (ANM) which prevents DoS attacks.