The Use of Wireless Networks is on the rise and many organizations are deploying WLANs to support their critical business applications. With the rising demand and use of wireless local area networks and the subsequent implementation of these networks by organizations, enterprises have been exposed to a lot of challenges and we have seen an increase in cybercrime and most of these attacks have been launched from wireless networks. Therefore, in this paper we will investigate the security threats and vulnerabilities that are there due to the inherent open nature of wireless communications and come up with an effective defense mechanism that will improve the wireless network security. The open system authentication architecture will be subjected to penetration tests and the results will be compared with those from other schemes like the pre- RSN and RSN methods to select the best model for WLAN authentication. The results inferred that the proposed model of authentication that is achieved by adding a nonce to the access point and therefore referred to as access point nonce (APN) authentication scheme is more effective and offer better security.