The present invention discloses a method for securely adding a new end station to a local area network (LAN) segmented into a number of virtual local area networks (VLANs). The invention is applicable to various types of LANs such as Ethernet and token ring. The LAN comprises an authentication server (AS) which interacts with each new end station before connection to a VLAN is allowed. The method involves the AS administering a test to the new end station, which may involve prompting the new end station for a password or asking it to encrypt a given number using a secret algorithm known only to the new end station and to the AS. The AS examines the results of this test and determines whether the new end station is permitted to join the VLAN. For added security, the new end station can verify authenticity of the AS by administering a test of its own, which may consist of prompting the AS for a password of its own or asking it to encrypt a new number, the new end station subsequently determining whether the AS is indeed genuine before beginning to transmit any further information. In this way, an end station cannot join a VLAN without authentication by the AS and a legitimate end station can verify whether the test it is asked to pass comes from a legitimate source, thereby avoiding network security breaches.