blocking yahoo and msn messenger 1

[cisco2511]

I have a LAN connected by DSL to the Internet.
All PC's have access to the internet. Could you help me with a utility with which i could block messengers and chat

Thanks in advance
Parasuram

 

[tolstoy]

You will need to block those ports at the firewall level. Take a look at the list of IANA's registered port numbers. There you will see what port AIM, MSN messenger, ICQ, etc. run on, and what protocol (udp,tcp). Close these ports at the firewall or router and you should be fine.

 

[tolstoy]

Keep in mind though that crafty users will always find ways around these things. I work at a school, and no matter what we block, there's always some other service that takes its place. For instance AIM has a web based interface that runs over port 80. In a case like this, you will need to block packets from that one domain, which may cut out half, if not most of AOL, which makes for ugly, mad users.