Friday, 3 August 2007

What is Telnet and SSH?

What is Telnet and SSH?
Telnet and SSH allows you to access your shell account.

Are there any differences between TELNET and SSH?
TELNET and SSH has long been employed by end-users and system administers to remotely control his or her servers. The key differences is that TELNET establishes a plain text connection while SSH, or Secure Shell, uses an encrypted connection so no one can ears drop on what data is being received or sent.

If you need to connect to the web server hosting your web site then SSH is the better option of the two since security is always a major concern, particularly, for businesses. Also, you do not want to legally liable for any damage that may occur from your web hosting account being used for illegal activities.

Why SSH?
When you telnet to a machine and, say, type your password, every keypress of your password is relayed across the Internet to our server in cleartext. This means that if some nefarious person on one of the routers through which the information passes sniffed the packets (the Internet equivalent of "tapping" a phoneline), then they'd suddenly know your password, letter for letter!
With SSH, the information is encrypted. So when you type your password, each letter is "scrambled" before it's sent over the Internet, and decoded at the other end. The encryption method is such that, if someone in between the servers stumbled upon the information, they'd just see a jumbled noise.

As you might imagine, this increases your security significantly.

Port (Ftp): 20 & 21
Port (SSH): 22
Port (Telnet): 23

Where can I get an SSH client? (For Windows Platforms)
Putty is a small but fully featured Windows SSH and telnet client. http://support.positive-internet.com/software.php
UNIX:
1. Command for SSH ?
ssh user@host

2. Can I run backups over ssh?
Yes. The easiest possible way to do this is:
# tar cvf - ssh user@host "dd of=/dev/tape"

3. Can I use ssh to communicate across a firewall?
Yes. All you need is an open port on the firewall and the sshd or sshd2 listening on the other side. Most people do this on port 22 (the standard port for Secure Shell), but if you have a BOFH, you can also tunnel through another open port through the firewall (I'm sure all those system admins love me now :-) by running a daemon on the remote side on a port that's allowed through a firewall, like SSL (port 443).

Set up the remote daemon running sshd on port 443:
# sshd -p 443

Then, on your local system, open a connection on port 443:
$ ssh -p 443 remotehost.example.org

You can also use Secure Shell to tunnel insecure traffic like POP, IMAP, and others through the firewall as well.

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