Telnet access is insecure because Telnet has no secure authentication mode and the data transmitted over Transmission Control Protocol (TCP) is in plaintext. If only Telnet is used, the system is vulnerable to denial of service (DoS), IP address spoofing, and route spoofing attacks.
As network security becomes more and more critical, using Telnet and File Transfer Protocol (FTP) to transmit passwords and data in plaintext proves to be more and more vulnerable. Secure Shell (SSH) resolves this issue by encrypting the transmitted data, providing secure remote login and other secure services.
SSH exchanges data using TCP. It builds a secure channel over TCP. In addition to the standard port (port 22), SSH supports access from other service ports to prevent unauthorized access.
SSH has three versions: SSH1.0, SSH1.5, and SSH2.0. The NetEngine 8000 F supports SSH2.0 that features backward compatible with SSH1.5.
Unless otherwise specified, SSH in this document refers to SSH2.0.