RE: Internet filtering at the packet level?

["Billy Dodson" <billy () pmm-i com>]

If your running linux anyway, you should look into Squid Proxy for
linux.  It is a Proxy server/Caching engine that runs on linux.
http://www.squid-cache.org  It has the logging and reporting that I
think you might be looking for.




-----Original Message-----
From: Rob Creely [mailto:programmingart () gmail com] 
Sent: Saturday, August 21, 2004 5:51 PM
To: Will - Security Engine
Cc: security-basics () securityfocus com
Subject: Re: Internet filtering at the packet level?

Any reason you can't just block all outgoing traffic except traffic to
your proxy server which is doing the filtering?

I think you looking at a lot of overhead and network slowdown by
scanning every single packet.  How about the people that connect to a
secure web proxy via SSL?  How about people that use SSH forwarding to a
web proxy?  You can't examine those packets, they are encypted.

Just my 2 cents.....

Cheers.

--Rob 

On Tue, 17 Aug 2004 14:51:25 -0500, Will - Security Engine
<security () the-engine org> wrote:
> Ok, I was wondering if it was feasable to filter internet access at 
> the packet level.  Here is the scenario.
>
> Small college campus - lets say 500 live on campus.  About half that 
> has internet access.  Then you also have the computer lab, with 16 
> computers.  Each teacher has a computer in their office as well, and 
> the CIS dept has about 30 or so computers in use.
>
> The filtering would be done on a Linux server using TCPDump.  I know 
> how to implement flags for content checking (If the phrase "hot monkey
sex"
> comes up in a packet, the user is flagged and traffic for that user 
> would be logged for a set period of time for reviewing later).  What I

> don't know is how to actually stop the traffic - but we won't worry 
> about that for now.
>
> Is there any problems with this?  Is it feasable?  How about just the 
> flagging portion of it, rather than the actual content blocking?
>
> I'm a student at a private baptist college that gets it's internet 
> access through MOREnet.  They require that we filter the content in 
> order to use their services.  Currently we only use a URL keyword and 
> blacklist filtering system (from my own tests), but it's obvious that 
> anybody who is serious about getting around the filter will have no 
> problem (web proxies are stupid easy to set up yourself, and P2P isn't

> filtered).  I'm worried that at some point it will come up that we 
> aren't doing a good enough job filtering, so we'd need a new solution.
> I think the packet-based system would be more accurate.  I would be 
> more inclined to not actually block the content that gets flagged.  I 
> would rather know that the user is accessing content ruled against by 
> the ToS and confront them on the issue.
>
> Lets not turn this into a censorship debate please ;)
>
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