Using TCP Wrappers you can control telnet, ftp and other services,
granting access to specific IPs or ranges.

Install freeware.tcp_wrappers.rte, from the Bull repository of freeware
http://www.bullfreeware.com (http://www.bullfreeware.com).

Edit /etc/inetd.conf as follows:

##ftp     stream  tcp    nowait  root    /usr/sbin/ftpd         ftpd -l -d -u 027 -t 900 -T 900
ftp     stream  tcp    nowait  root    /usr/local/bin/tcpd  ftpd -l -d -u 027 -t 900 -T 900
## telnet  stream  tcp    nowait  root    /usr/sbin/telnetd      telnetd -a
telnet  stream  tcp    nowait  root    /usr/local/bin/tcpd  telnetd -a


Create /etc/hosts.deny and /etc/hosts.allow to control access, like this:

echo "ALL: ALL" > /etc/hosts.deny
echo "ALL: 127." > /etc/hosts.allow


And add whatever addresses you require to allow:

echo "ALL: 10.100.0.3" >> /etc/hosts.allow
echo "telnetd: 192.168.0." >> /etc/hosts.allow
echo "ftpd: 172.16." >> /etc/hosts.allow
...