The article discusses the problem of ensuring information security with remote access to information resources. The relevance of the work is due to the growth of distributed computer systems and the high risks of data interception during the transfer of credentials. The functions of the remote access server and the basic Point-to-Point Protocol link layer are analyzed. The main focus is on the classification and comparison of authentication protocols: direct scheme (PAP, CHAP, S/Key) and indirect (centralized) scheme (RADIUS, Kerberos). The article describes in detail the algorithms of each protocol. As a result of the research, the necessity of a combined approach to the choice of authentication protocols depending on the network architecture is substantiated, as well as the requirements for modern remote access systems are formulated.