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Block port 25 for training

Posted on 2008-10-08
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Last Modified: 2012-05-05
I'm a trainer part time and have consistently to be patient and put up with folk claiming they're paying attention while I know they're e-mailing. I'm good at my job and give good and interesting lessons but other than taking my clothes off to illicit attention I'd like a safe way to block and unblock port 25 during class remembering that I'm sometimes at a client site.



Any suggestions would be appreciated and also help those with mild ADD learn Excel, Word etc.
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Question by:macmic
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11 Comments
 
LVL 17

Expert Comment

by:Andres Perales
ID: 22669123
well if you are using a mobile classroom that has a closed network you can put a firewall in place between the clients network port that they give you for access and the switch where your test boxes would hook into...
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Author Comment

by:macmic
ID: 22669215
No, I can't interfere with others networks too much. I'm thinking either Windows firewall or group policy. something I can quickly add and remove. Cheers though
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LVL 17

Expert Comment

by:Andres Perales
ID: 22669282
Windows firewall would work as long as the user accounts the users are using do not have admin rights to the change the windows firewall, are all of these boxes windows xp or vista boxes?  If so you can consider Steadystate....
http://www.microsoft.com/windows/products/winfamily/sharedaccess/default.mspx
 
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LVL 10

Expert Comment

by:kukno
ID: 22669409
Hi,

use WinArpSpoofer, to "announce/mask" the trainer PC/Laptop as the default gateway. Then all packtes of the clients will be routed to your PC. You can then decide what to do with them. Assuming you can run a decent firewall on your PC, you could simply drop SMTP and re-route the rest to the legitimate router.

     http://www.nextsecurity.net/software/Windows_ARP_Spoofer.html

Here is a list with some other arp poisioning tools.

http://www.l0t3k.org/security/tools/arp/

Regards
Kurt
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Author Comment

by:macmic
ID: 22669975
Yeah in our own office that would be cool but I can't add software to computers at client sites. Good recommend though for future stuff
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Author Comment

by:macmic
ID: 22670013
kukno - yeah but for a client site I'd be tampering on their network. I'd just like a sneaky yet acceptable block on the individual PC if you get my gist
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LVL 4

Expert Comment

by:Interserv
ID: 22670249
you would want to block port 80 and 443 as well because hotmail, gmail, Outlook Web Access and many more use the web and not port 25 for email.  You could do this with a GPO by setting up a proxy or adding an ip in the proxy settings that does not exist.  Just remember if you set up a proxy using GPO, you need to manually remove the proxy settings when you stop enforcing the GPO.
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Author Comment

by:macmic
ID: 22670604
Interserv: how to using GPO mate?
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LVL 10

Expert Comment

by:kukno
ID: 22699745
>I'd just like a sneaky yet acceptable block on the individual PC if you get my gist

o.k., then block the ports with the IPSEC subsystem.

http://support.microsoft.com/kb/813878

HOWEVER: You must install ipseccmd.exe and possibly netdiag on the clients!

http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=7D40460C-A069-412E-A015-A2AB904B7361

Filter for port 25 should be:

IPSeccmd.exe -w REG -p "Block SMTP" -r "Block Outbound SMTP" -f 0=*:25:TCP -n BLOCK


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LVL 10

Expert Comment

by:kukno
ID: 22699804
running ipseccmd.exe from a USB stick is actually not "installing" any software.
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LVL 10

Accepted Solution

by:
kukno earned 1500 total points
ID: 22699808
running ipseccmd.exe from a USB stick is actually not "installing" any software.
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