hosts.deny

vim /etc/hosts.deny

sshd: a.b.c.0/255.255.255.0

sshd: *.xyz.net

sshd: *.*.*.us

sshd: *.*.*.cn

sshd: m.n.0.0/255.255.0.0 

/etc/rc.d/init.d/sshd restart

# /etc/rc.d/init.d/xinetd restart

# /etc/rc.d/init.d/network restart