16 Chapter 16. Telnet security In this chapter, we explain how to implement and use the security features of the z/OS TN3270 server. The server supports native connection security through data overrun protection, network access control, and basic Transport Layer Security (TLS) functions. It also supports Application Transparent Transport Layer Security (AT-TLS) through configuration of the policy agent. It is defined as a controlling application when set up in AT-TLS support mode. We discuss the following topics in this chapter.