SSH

http://www.youtube.com/watch?v=0YAHuCZ_NM4&feature=related

http://www.youtube.com/watch?v=r_wW8N-wz7c

http://www.youtube.com/watch?v=kUZRQXLSFwc

http://www.youtube.com/watch?v=_NcMWHumRoA&list=PLD8234B9EC8FB7DB3&index=61&feature=plpp_video

/etc/ssh/sshd_config 
PermitRootLogin no
AllowUsers user101 user102

AllowUsers fulano@10.1.1.1 mengano@10.1.1.1 fulano@10.2.2.1 mengano@10.2.2.1
DenyUsers user114 user115

/etc/hosts.deny
$ cat /etc/hosts.deny
#
# hosts.deny    This file describes the names of the hosts which are
#        *not* allowed to use the local INET services, as decided
#        by the '/usr/sbin/tcpd' server.
#
# The portmap line is redundant, but it is left to remind you that
# the new secure portmap uses hosts.deny and hosts.allow.  In particular
# you should know that NFS uses portmap!

sshd: all

sudo gedit /etc/hosts.deny

ALL: ALL
/etc/hosts.allow
$ cat /etc/hosts.allow
#
# hosts.allow This file describes the names of the hosts which are
#  allowed to use the local INET services, as decided
#  by the '/usr/sbin/tcpd' server.
#
sshd: 93.42.132.43 86.34.22.122

sudo gedit /etc/hosts.allow 


sshd: 192.168.0.10 # Permitir una dirección.
sshd: 192.168.0.*  # Permitir todo el rango de la IP 192.168.0.1 a 192.168.0.255.

sudo gedit /etc/ssh/sshd_config 

MaxAuthTries 2 

MaxStartUps 3