The simplest remote logon method-Telnet Service

In our eyes, hackers are quite mysterious. They seem to be able to take things from the air and remotely manipulate our computers in unknown places. Then, the Telnet service can complete the simplest intrusion means. Many friends seem not familiar with this, so they may have doubts. After telnet to another server! What can we do? What command should I use?

Telnet Introduction

Telnet is used for remote logon to the Internet. it allows users to sit on the keyboard of an Internet-connected computer and access the computer of another Internet-connected computer through the network. this connection can happen on a computer in the same room or on a computer that has been connected to the Internet all over the world. traditionally, a computer connected to a computer that provides services to all users on the network is called a server, and a machine in use is called a client ). once connected, the client can enjoy all the services provided by the server. you can run a common interaction process (register and run commands) or access many special servers, such as searching for book indexes. various services provided by different hosts on the Internet can be used.

The simplest way to use Telnet is to type in the command line:

%telnet remote-computer-name(or IP)

Here the C shell of UNIX system is used, because the command is set to "% ". if other computer systems (such as OS, VAX/VMS, and Macintosh) commands are used, there are only some differences in details, but they are essentially the same, the following is an example of the basic Telnet Service:

telnet porky.math.ukans.edu
Trying 129.237.128.11...
Connected to porky.math.ukans.edu.
Escape character is '^]'.
SunOS UNIX(porky)
login:wl
passwordxxxxxx
Last Login: Tue Mar 28 05:35 from ns.bta.net.cn
SunOS Release 4.1.3_U1(SLIPPERY1) #3: Sun Nov 20 23:47:23 CST 1999
No match.
if:Expression syntax.
porky/serv/wl%ls
hello
porky/serv/wl%
porky/serv/wlí/
porky/%ls
Mail/ dev/ home/ mnt/ sbin/
usr/
News/ domain/ home1/ net/ serv/
var/
Record/ etc/ kadb* pcfs/ sys@
vmunix*
bin@ export/ lib@ print tmp/
boot gofer/ lost+found/ record tmp_mnt/
porky/%

The above example is to use the Telnet service to find a remote computer called porky.math.ukans.edu. after finding this computer, the computer that has been online has become a terminal. the dialog displayed on the screen is the same as the terminal connected to the user on the host. the user must register to enter (login) and log out (logout ). after login, You can provide any commands suitable for remote systems. Because "porky.math.ukans.edu" is oriented to UNIX systems, all standard UNIX Commands (like ls and pwd) can be used. when you exit from the remote system, you can also exit from Telnet to run your local system. in fact, Telnet is a tool that can be registered to the remote computer system.

How the Telnet service works

What happens when Telnet is started? An application system consists of two parts: "client" -- this is the client mentioned in Telnet introduction, and the other part is "server" -- this is the system that provides services on a network computer, it is called a server. the Network is a Server that uses TCP and UDP) is a tool that provides communication between the two Clinet and Server.

The client must do the following:

(1) Establish a TCP connection between the network and the server

(2) receiving input in a convenient way

(3) Some standard formatting inputs are reformatted and re-formatted and transmitted to the server.

(4) Accept the output from the server in some standard formatting

(5) reformat the output displayed to you

Server software is a system that runs on a host to provide services. If a service system is not running, it cannot provide services.

If a service is called, it can:

(1) notify the network software to prepare the connection;

(2) Wait for the emergence of a standard formatting requirement;

(3) Service requests;

(4) deliver a standard format result to the customer;

(5) wait again

A server should be able to handle various customers, some running on similar computers, and some running on different machines such as IBM/PCs, macdeskshes, and Amigas. to achieve this, the server must have a set of communication rules, which are usually called protocols. because the Telnet service is used between two application layers, it is called the application layer protocol. anyone can compile a client on any type of computer. the client can access the server as long as it can communicate online and follow the protocol. in fact, the user's Macintosh can use Telnet and other Internet tools, so that many different systems can work for it.

In terms of usage, an application layer protocol usually allows the client and the server to have different data settings and notifies the client and the server to communicate with each other. these are often completed by several byte text programs at the beginning of each line. if the server sends a line command starting with "TXT" to the customer, other data after "TXT" is sent to the screen for display. if a line starts with "CMD", it indicates that the information is from the service software to the customer software. the user cannot see this because these control signals are removed when the information is sent.