Chapter 5 : Application Layer (part 1)

1.       Telnet

Telnet is a network protocol used to establish a connection with a remote device, typically a server or a computer, over a TCP/IP network. It allows users to access and communicate with the remote device's command-line interface as if they were physically present at the device. However, Telnet transmits data, including passwords, in plaintext, making it insecure. As a result, it's largely been replaced by more secure protocols like SSH (Secure Shell).

2.       Rlogin

RLogin is a network protocol used for remote login to systems, similar to Telnet. It allows users to access the command-line interface of a remote system. However, RLogin is less common and less widely supported compared to other protocols like Telnet or SSH. It lacks the robust security features of SSH and is not recommended for use over untrusted networks due to its vulnerability to eavesdropping and data interception. As a result, SSH is typically preferred for secure remote access to systems.

3.       SSH

SSH, which stands for Secure Shell, is a cryptographic network protocol used for secure communication over an unsecured network. It provides a secure channel over an insecure network by using encryption and authentication methods to ensure the confidentiality and integrity of data exchanged between two networked devices.

SSH allows: 

Secure Communication: SSH encrypts all data transmitted between the client and server, including passwords, commands, and data, effectively protecting it from eavesdropping and interception.

Authentication: SSH supports various authentication methods, including passwords, public-key cryptography, and keyboard-interactive authentication. Public-key authentication is widely used and offers a higher level of security compared to password-based authentication.

Key Exchange: SSH uses cryptographic algorithms to establish a secure connection between the client and server. During the connection setup, SSH negotiates encryption algorithms, integrity algorithms, and key exchange algorithms to ensure secure communication.

Port Forwarding: SSH supports port forwarding, also known as SSH tunneling, allowing users to securely access services running on remote servers as if they were locally available.

Overall, SSH is widely used in various environments, including system administration, software development, and network security, due to its robust security features and versatility in securely accessing and managing remote systems and resources.

4.       FTP

FTP, or File Transfer Protocol, is a standard network protocol used for transferring files between a client and a server on a computer network. It operates on the application layer of the TCP/IP protocol suite and relies on two separate connections: a control connection for sending commands and receiving responses, and a data connection for transferring files.

5.       TFTP

TFTP, or Trivial File Transfer Protocol, is a simple file transfer protocol used for transferring files between a client and a server on a computer network. It's a lightweight protocol designed for minimal resource consumption and ease of implementation, making it suitable for transferring small files in embedded systems, network booting, and firmware updates.

6.       RCP

RCP, or Remote Copy Protocol, is a network protocol used for copying files between computers on a network. It is part of the Berkeley r-commands suite, which also includes protocols like rlogin and rsh. RCP provides a simple method for copying files between remote hosts, similar to the cp command used for copying files locally.

RCP provides a simple and straightforward method for copying files between remote hosts, its lack of security features makes it unsuitable for use over untrusted networks. Organizations and users concerned about security should consider using more secure alternatives such as SCP or SFTP for remote file transfer tasks.

7.       SCP

SCP, which stands for Secure Copy Protocol, is a network protocol used for securely transferring files between a local host and a remote host or between two remote hosts. It is a part of the SSH (Secure Shell) suite of protocols and provides encrypted file transfer capabilities, ensuring the confidentiality and integrity of data exchanged over the network.

Reference 
Andrew S. Tanenbaum, and David J. Wetherall, Computer Networks, 5th Edition, China Machine Press, 2011.