Different between Telnet/SSH/FTP

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Telnet vs SSH

    Secure Shell, commonly known as SSH, and Telnet are two network protocols that have been used widely at one point in time or another. They are both used to connect to remote servers in order to facilitate some sort of communications. The primary difference, which also led to one superseding the other, is in security. SSH offers security mechanisms that protect the users against anyone with malicious intent while Telnet has no security measures whatsoever.

    Telnet was designed to work within a private network and not across a public network where threats can appear. Because of this, all the data is transmitted in plain text, including passwords. This is a major security issue and the developers of SSH used encryptions to make it harder for other people to sniff the password and other relevant information. Telnet also omits another safety measure called authentication. This ensures that the source of the data is still the same device and not another computer. Without authentication, another person can intercept the communication and do what he wishes. This is also addressed in SSH as it uses a public key to authenticate the source of the data.

    Due to the security measures that were necessary for SSH to be used in public networks, each packet contains less data to make room for the data of the security mechanisms. In order to transmit the same amount of data, you would need to take-up a lot more bandwidth. This is called overhead and was such a major issue back when internet speeds were very low because it translates to a performance hit.

    The security issues of Telnet forced a lot of people to use SSH in order to protect themselves. It didn’t take a long time before SSH replaced Telnet in a great majority of its uses. Telnet did not fade away though as it is still used in some areas, mostly in testing and debugging. Telnet extensions were developed to provide security but they are not used in most Telnet implementations.

Summary:
1. SSH and Telnet commonly serves the same purpose
2. SSH is more secure compared to Telnet
3. SSH encrypts the data while Telnet sends data in plain text
4. SSH uses a public key for authentication while Telnet does not use any authentication
5. SSH adds a bit more overhead to the bandwidth compared to Telnet
6. Telnet has been all but replaced by SSH in almost all uses

FTP vs. Telnet

    FTP and Telnet are two very old protocols, that are used on networks to add certain functionalities. FTP is a File Transfer Protocol, and its only concern is to facilitate the transfer of files from one point to another, along with a few management capabilities like making and deleting directories. Telnet is a bit more like a ‘jack of all trades’, as it is simply a connection protocol that allows a user to connect to a remote server that is listening for Telnet commands. Once the connection is established, the user can then issue commands to the server computer, and examine the responses that are sent back.

    Although both started out as command line tools, GUIs later appeared that greatly simplified the use of FTP. Instead of knowing all the commands and typing out all the filenames, some dedicated applications let you browse a local drive and a remote drive, as if you are using a file explorer. It keeps all the commands invisible to the user, thereby lessening the learning curve. This is not really possible with Telnet, as there are a wide range of commands and parameters that can be issued to the server.

    Due to the age of both software, they do not have any built-in security measures. Even usernames and passwords are sent in plain text, making them vulnerable to sniffing. With later modifications, people can now use secure versions of FTP, called FTPS and SFTP. On the other hand, Telnet has been largely replaced by SSH, due to the addition of security measures. As Telnet has been superseded by SSH, making it secure seems redundant.

    Currently, FTP is still in wide use, as it is an easy way to upload files to web servers. There’s a wide array of applications that use FTP to achieve their purpose. The use of Telnet has been dwindling since the creation of SSH, but there are still people who use it mainly as a diagnostic tool. Telnet provides a good view of how certain network services work, by sending commands and examining the response to determine if it is proper or not.

Summary:
1. FTP is a protocol used specifically for transferring files to a remote location, while Telnet allows a user to issue commands remotely.
2. FTP can be used with a command line, a dedicated application, and even with most web browsers, while Telnet is restricted to the command line.
3. There are ways to use FTP in a secure environment, while Telnet will always be unsecured.
4. FTP is a well-known and reliable method of uploading files to web servers, while Telnet is now commonly used in diagnosing network services.

原文地址：https://www.cnblogs.com/dirge/p/9568575.html