Remote logon protocol (Telnet, rlogin, ssh)

1) Telnet (Telecommunication Network Protocol)

Telnet enables communication between the client and the server through option negotiation.

As shown in, the Telnet client process interacts with the Terminal Driver and TCP/IP module to transmit information.

The Telnet service process is responsible for data interaction with Pseudo Terminal drivers and TCP/IP. The so-called terminal driver is to implement a shell program, the effect is the same as directly using the local terminal to input commands and directly execute.

2) Rlogin

Rlogin was originally a remote logon protocol in UNIX systems. The client process and server process have already known the operating system type of the other Party in advance, thus saving the option negotiation mechanism.

In general, it is similar to the Telnet protocol, but the internal implementation is relatively simple.

 

3) SSH (Secure Shell)

The telnet and rlogin programs described above have security vulnerabilities in the transmission mechanism because they use the plaintext Mechanism during data transmission. If someone intercepts such data on the network, then some important data will inevitably be leaked.

SSH has two advantages: (1) SSH is a reliable protocol for remote logon and other security services. It uses data encryption mechanisms to prevent DNS Spoofing and IP spoofing. (2) The transmitted data is compressed, which speeds up transmission.

SSH protocol is a security protocol built on the application layer and transport layer. It consists of three parts: (1) Transport Layer Protocol content, providing authentication, data integrity check, and other functions. (2) user authentication protocol layer, which runs on the transmission layer and implements Identity Authentication during communication. authentication methods include password authentication and key authentication. (3) The connection protocol layer allocates the encrypted channel to the logical channel and runs on the user authentication protocol layer.

The SSH protocol can be replaced by some traditional network program protocols such as telnet and FTP, providing a reliable data protection mechanism in an insecure communication environment.