accessing my linux box via telnet

[Tim Chase]

> I need to access my linux box using telnet to be able to reach
> it when I'm not next to it, how do I do?

There are a couple factors that play into an answer, so to answer 
the question one would need to know:

1) do you have to use telnet, or can you use ssh?  Using SSH is 
much preferred because it encrypts your password over the network 
unlike telnet which sends it in plain-text over the wire.  MUCH 
preferred.  Telnet might be fine for a fixed server of data such 
as a weather server, IRC, or a MUD where there's no password to 
be sent.  So unless there's some overly compelling reason to use 
telnet (such as perhaps ssh/putty not being accessible to a 
screen reader, or severe lock-down of the guest machine 
preventing you from installing putty or the cygwin ssh utilities) 
I strongly recommend SSH instead.

2) is your PC behind a hardware router/firewall?  If so, you 
likely have a private IP address of the form 192.168.x.y and a 
public/external IP address.  You can find your internal IP 
address with the "ifconfig" command.  You can find your external 
IP address by browsing to www.whatsmyip.org.  If the two numbers 
aren't the same, there are more hoops to jump through.

3) is your guest machine also on your same home network, or are 
you accessing it from outside your LAN?

If the answer to #3 is that you're just on your home network, it 
obviates most of the problems with telnet vs. ssh and doesn't 
need reconfiguration of your router/firewall.

The simple answer to #1 is that you can start either the sshd or 
the telnetd program either on startup or you can manually start 
them (or both, so you don't have to reboot, but it will come up 
the next time you boot).  Alternatively, they can be started on 
demand via the inetd superserver.  Depending on your distro, 
there may be a spiffy interface for this sorta thing.  I think 
when I installed the openssh package under Debian, it asked if I 
wanted sshd to run on startup, and I answered yes.

As to the second question, if you're not behind a 
router/firewall, you're good to go.

If you *are* behind a router/firewall, you have to configure it 
to take incoming traffic on the associated port (22 for ssh, 23 
for telnet) and forward it to the same port on your machine.

This usually involves specifying that the router/firewall assign 
a fixed IP address to your machine based on its MAC address. 
This is helpful so it knows where to forward traffic and so it 
prevents other private IP addresses from being assigned to your box.

You then have to use your router's configuration tools to set up 
port forwarding.  These days, most of them allow you to browse to 
http://192.168.0.1 or http://192.168.1.1 (though you might have 
to use "https" instead of "http").  Each router's configuration 
software is different.  However, you'd be poking around for a 
"port fowarding" or "NAT" ("network address translation") option. 
  You configure traffic coming from external port 22/23 to go to 
the same port on your internal machine (identified by its static 
IP address).

Hope this helps,

-tim