RE: Internet filtering at the packet level?

From: Billy Dodson (billy_at_pmm-i.com)
Date: 08/23/04

  • Next message: Andreas: "Re: Blocking Access to Non-domain computers" 
    Date: Mon, 23 Aug 2004 14:06:28 -0500
To: <security-basics@securityfocus.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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