This might not be secure: Giving away version numbers is often not a smart
move on a machine that might be accessed from outside a secure network
as it can narrow down the options for an attacker to use. In fact, even
saying Ubuntu might be questionable for the same reason. For instances
when you want to take an extra step in obscuring your information, you can
edit the issue and issue.net files in your /etc directory to change
the message displayed.To use Telnet to connect to a different computer, use that computer’s IP
address on the network instead of using your own. You can use Telnet on
local networks and across the Internet to connect to any computer running the
server on an open port.
Telnet uses port 23, but you can use it with another port by adding that port to
the IP address, as in this example, which uses Telnet to connect to port 110 to
test a POP3 connection/server:
Click here to view code image
matthew@seymour:~$ telnet 192.168.1.102 110
Telnet Versus SSH
Although Telnet is worth keeping around as a fail-safe, last-resort option,
SSH is superior in nearly every way. Telnet is fast but also insecure. As stated
earlier, it sends all your text, including your password, in plain text that can
be read by anyone who has the right tools. SSH, on the other hand, encrypts
all your communication and so is more resource intensive but secure; even a
government security agency sniffing your packets for some reason would
have a hard time cracking the encryption.
Andy Green, posting to the fedora-list mailing list, summed up the
Telnet situation perfectly when he said, “As Telnet is universally
acknowledged to encourage evil, the service telnetd is not enabled by
default.” (© Andy Green) It is worthwhile taking the hint: Use Telnet as a last
resort only.
Setting Up an SSH Server
If SSH is not installed already, you can install the OpenSSH server by adding
the openssh-server package. As you might have guessed, sshd is the
name for the SSH server daemon.
Configure your firewall to allow connections through port 22. If this port is