block MSN chat during day

I have ISA running on Windows 2000 Advanced server. I block chating form 7 to 5 weekdays. Recently, MSN chat started working during the day.

What IP addresses do I need to block to stop the chating during the day.

 

I copied this out of the "Help" section of MSN Messenger.

For instant messaging

To allow your network users to have a direct connection to instant messaging services, you will need to:

Open outgoing TCP connections to Port 1863 on your proxy servers.
Let your network users know which kind of proxy server your network uses (HTTP, SOCKS4, or SOCKS5) and provide them with the corresponding details (server name, port number, and so forth) so they can enter that information on the Connection tab of the Options dialog box (Tools, Options).
Make sure the internal local area network has access to the Domain Name System (DNS) servers to resolve the names of external hosts such as messenger.msn.com.

For file transfer

Both incoming and outgoing TCP connections use this range of ports: 6891 to 6900. This allows up to 10 simultaneous file transfers per sender. If you open only Port 6891, users will be able to do only one file transfer at a time.

The TCP ports need to be configured so that sockets on a port remain open for extended periods of time.



>I have mixed feelings about blocking this service. CEOs need to realize how much phone traffic they reduce by allowing Messenger to run.<