Table of Contents
Secure Shell, ssh
The Secure Shell is basically an encrypted telnet, but it can do a lot more than telnet ever could such as tunnelling encrypted connections both in forward and reverse directions. Both clients and servers are available SSH on many operating systems.
System Banner
Also on the security front, further down sshd_config, consider adding a banner warning stating that the system is private and not for public access. In the unlikely event you are hacked and catch the culprit you will have a stronger legal case if you have told any intruders that they should not be there.
. # banner path Banner /etc/issue
/etc/issue
is displayed on a console before login, sometimes a /etc/issue.net
is present in case you want to have a different warning for local console users compared to network login users. Bear in mind that ssh -q will not show a banner so don't rely on just this alone as a security warning.
/etc/motd
(Message Of The Day) is displayed after a successful login, so any system specific info should go there and not in /etc/issue
.
After having done this change, you will need to stop (not just restart sshd) with
/etc/rc.d/rc.sshd stop
and /etc/rc.d/rc.sshd start
And the result? Success!!
zeus:~ andrewst$ ssh 192.168.1.1 -l andrew andrew@192.168.1.1's password: Last login: Tue Apr 20 00:56:35 2004 from 192.168.1.21 Linux 2.4.25. Welcome to Slackware! andrew@corerouter:~$
Enable TCP keep alives
Add the following to /etc/ssh/sshd_config to prevent inactivity causing a firewall terminating a session:-
TCPKeepAlive yes KeepAlive yes ClientAliveInterval 60
SSH tunnels
ssh -L localhost:5222:myxmpp.mydomain.co.uk:5222 -p 443 user@proxy.server.co.uk ssh -L localhost:222:ssh.mydomain.co.uk:22 -L localhost:10022:midpoint.myserver.com:22 -p 443 user@proxy.server.co.uk
Socks Server
ssh -D 1080 -p 443 user@my.server.com