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TN5250 or, Telnet 5250, is a form of Telnet service for letting users access AS/400 systems over a TCP/IP network using a TN5250 client terminal emulator.

What is TN5250?

TN5250, also known as Telnet 5250, is a specialized form of Telnet designed to allow users to access AS/400 systems over a TCP/IP network. Acting as the counterpart to TN3270 for mainframe systems, TN5250 facilitates seamless interaction between TN5250 clients and AS/400 systems, complete with full 5250 terminal emulation.


How It Works

TN5250 (Telnet 5250) is to the AS/400 what TN3270 is to the mainframe. A TN5250 service included with Microsoft SNA Server lets TN5250 clients connect to AS/400 systems using SNA Server without installing TCP/IP on the AS/400. TN5250 offers full 5250 terminal emulation, including hot backup and security features similar to those included with the TN3270 service.

TN5250 provides 5250 workstation emulation that supports almost all the field attributes and keyboard sequences of a “real” SNA 5250 except text assist. TN5250 has a natural and intuitive look and feel; no conversion is required inside the AS/400. TN5250 provides workstation emulation only and does not include file-transfer or printer-emulation services.

Key Features of TN5250

  • Hot Backup: Like its mainframe cousin TN3270, TN5250 also offers hot backup features.
  • Security: TN5250 includes security protocols similar to those provided by TN3270.


TN5250 is strictly for workstation emulation and does not support file-transfer or printer-emulation services. Additionally, it lacks support for text assist.

Modern Alternatives

While TN5250 is still used in some legacy environments, there are more modern alternatives that offer additional functionalities. Solutions like SSH offer encrypted connections and broader compatibility, and specialized AS/400 access solutions now offer integrated file-transfer and printer-emulation services.

SSH for AS/400 Systems

SSH provides a secure, encrypted connection between the client and server, making it a popular choice for accessing AS/400 systems today.

Integrated Access Solutions

Newer solutions offer a more comprehensive set of services including file transfer and printer emulation, all integrated into a single client software package.


TN5250 remains an essential tool for interacting with AS/400 systems, especially for those who require full 5250 terminal emulation. However, the landscape has evolved, and modern alternatives now provide more functionalities with enhanced security features.