hosts.deny

#CentOS

/etc/hosts.deny
[1]
sshd: a.b.c.0/255.255.255.0
sshd: d.e.f.0/255.255.255.0
sshd: g.h.i.0/255.255.255.0
[2]
sshd: a.b.c.0/255.255.255.0, d.e.f.0/255.255.255.0, g.h.i.0/255.255.255.0
/etc/rc.d/init.d/sshd restart
# /etc/rc.d/init.d/xinetd restart
# /etc/rc.d/init.d/network restart