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A Guide to Telnet

What is Telnet?

Telnet is a protocol for one computer to talk to another computer over a network. In most situations today, that means that the PC on your desk is talking to another computer, and acting like a terminal. Thus 'telnet' is sometimes used interchangeably with 'terminal emulation'.

The Telnet protocol connects your local PC (the client end) with a remote system (the server or host) through a network port, usually port 23. This allows you to work remotely within the server’s environment and on applications that run on a server.

Do I need a Telnet program?

The easy answer is that if you need it, you'll know it. But I'll try to be more helpful. If you know you want to access a service or a remote server application, and their information states that you access it via telnet, you need one. If you're browsing the web, and you point your browser to a cross-link that starts out 'telnet://' instead of 'http://', you need one.

You may have one already installed as part of your Windows operating system (one comes with all versions of Windows), however the telnet client shipped with Windows is designed to work with a limited terminal emulation type and does not support many other common terminal emulation functions.

What else do I need to Telnet across the Internet?

For Anzio to communicate over the Internet, a PC supporting a network connection or a PC with a modem connection to the Internet is first needed. It must already be connected to the outside world in order for the Telnet protocol to work.

If you are connecting to a company network, rather than the outside world, you still need a currently working network connection before running Anzio.

That’s it. Pretty simple - until you take a look at ‘security’.

What are the security issues?

The Telnet protocol by itself is quite simple. But that means it is quite susceptible to prying eyes. No data transmitting between the two machines is secure or encrypted, including login information, printed information and even data destined for the screen.

Because of this, you may run into obstacles trying to use the Telnet protocol from your local office or home. First, most personal firewall and Internet Security Suites, will block the network port in which a telnet client uses to connect to a remote system. Second, because of the security issues with the telnet protocol, many routers and firewalls block the telnet port from gaining access to the outside world. And finally, many ISP’s will block the telnet protocol and the default network port it uses.

What’s a host name?

The computer that your PC connects to is referred to as 'the host'. It may be within your company, or it may be somewhere out on the Internet, such as a library system or a medical reference service.

Is the host name the same as my ISP name?

No, in most cases.

Your Internet Service Provider (ISP) is the company that gives you access to the Internet. It may be a local company. It may be a nationwide service such as ATT's WorldNet that gives you only a point of connection. It may be a large Internet service that also provides content, such as MSN or Netcom. Or it could be one of the older online services that now allows Internet connection, such as CompuServe or AOL. The important thing to remember is that who you're connected THROUGH is not necessarily who you're connected TO (but it could be).

Let's look at a typical scenario. Assume that you connect to the Internet through ''. This is your Internet Service Provider (ISP). It has a particular host name ( and an IP address (something like But you want to access a library named ''. This is your intended host. It also has an IP address, but you shouldn't have to worry about that.

How do I connect over the Internet?

In order to use the Telnet protocol over the Internet, you must already have an existing connection to the Internet. Often you can verify you are connected to the Internet by bringing up your web browser. If you are not connected, this often will force your network software to connect.

Once your web browser connects, you can then minimize your browser and begin working with Anzio.

We'll assume this connection has been made, as evidenced by the fact that you can run your web browser.

How do I use Anzio?

As a first step, click on the Anzio desktop icon to start Anzio. The first time you bring up Anzio, it will ask for a terminal type - if in doubt, choose 'VT220'.

A warning here is that your terminal type must be what the host and the host application requires. In order to work properly, all three must match – the host login, the host application and the settings in Anzio.

Anzio will then ask for a host name. This is the name of the system you want to connect TO, not THROUGH. In our example, it is '', not ''. Type in the name. Case doesn't matter ('BIGLIB.EDU' works fine). If you're lucky, you'll get a login prompt from the host system. From then on, you're on your own.

If Anzio can't connect using the name, there could be a problem with your PC's 'name resolution' (DNS) setup (but if your browser works, Anzio should work). In this case, if you know the host's IP address, try it.

What is the ‘port’?

Telnet connections ordinarily use port 23. This is part of the TCP/IP network protocol and has nothing to do with serial ports. The host system you're connecting to may for various reasons be set up at a different port number. If so, then when you specify the host name, add on the end a colon and the port number, such as ''. You can do the same after an IP number.

Can I launch Anzio automatically from my web browser?

Yes. When your web browser is pointed to a web page, and you click on a cross-link that starts with 'telnet://', your web browser will want to start an external telnet program. You can configure your web browser to use Anzio as its designated telnet program. You can set up Anzio to be your Windows default telnet client under Anzio’s Help menu. See Anzio's manual for more information.

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