iptables

vim /etc/sysconfig/iptables

service iptables restart

# Generated by iptables-save v1.3.5 on Wed Jan 12 14:51:15 2011

*filter

:INPUT ACCEPT [0:0]

:FORWARD ACCEPT [0:0]

:OUTPUT ACCEPT [4818:1515208]

:RH-Firewall-1-INPUT - [0:0]

-A INPUT -s a.b.c.0/255.255.255.0 -j DROP

-A INPUT -s x.y.0.0/255.255.0.0 -j DROP 

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