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Old 05-08-2007, 05:10 AM   #1
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Registered: Feb 2007
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Blocking msn,yahoo,giam,skype etc messanger

Dear All Linux Experts ,

I want to block instant messengers such as msn,yahoo,giam,skype etc
through iptables.

I want to block these IM during office time only(9am to 5 pm) and to specific computer or IP but want to open at 1pm to 2pm (lunch time).

How to put it in cron so that iptables blocks at 9am but open at 1pm automatically.

Please help me.
Old 05-08-2007, 11:16 PM   #2
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Location: San Jose, CA
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Note that most of these protocols are port-nimble. The only EFFECTIVE way to block them is to block ALL ports and require all traffic to go through a proxy. AIM is known to support several hundred ports, including ports 80, 110, 443, and others.

You could, however, block the default ports. You don't even need a cron job, iptables can use time as a criteria for matching, as shown here:
Old 05-09-2007, 12:14 AM   #3
Registered: Mar 2006
Distribution: RedHat, Slackware, Experimenting with FreeBSD
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Many of these IM programs can be tunneled through an authorized port to bypass restrictions. You may want to look up the Layer7 filtering project to overcome this.
Layer7 filtering takes a peek at the actual data inside a packet and can be used in conjuction with iptables to form policies.


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