Block Yahoo Messenger, AOL, MSN and ICQ using IPTABLES

If you’re a network administrator and you’re using Linux on your servers, you can stop the rest of the users from using IM applications by blocking their access to the most-used IM protocols:
ICQ and AOL:

# iptables -A FORWARD –dport 5190 -j DROP
# iptables -A FORWARD -d login.oscar.aol.com -j DROP

MSN:

# iptables -A FORWARD -p TCP –dport 1863 -j DROP
# iptables -A FORWARD -d 64.4.13.0/24 -j DROP

Yahoo Messenger:

# iptables -A FORWARD -p TCP –dport 5000:5010 -j REJECT
# iptables -A FORWARD -d cs.yahoo.com -j REJECT
# iptables -A FORWARD -b scsa.yahoo.com -j REJECT

IPTABLES - blocking IPs simplified

You can block an IP from IPTABLES by using

iptables -I INPUT -s 192.168.0.88 -j DROP

You can simplify things a little bit by using a shell script and a predefined text file containing the IPs we want to be blocked. Either create a new file or add the following at the end of the script which activates the firewall:

#!/bin/sh
for i in $(< bad_hosts.lst) ; do
iptables -I INPUT -i eth1 -s “$i” -j DROP
done

Now create a new file in the same directory and name it bad_hosts.lst and add a new IP to be blocked on every single line, like in the example below:
192.168.2.99
192.168.2.67
86.138.2.7