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Re: IPS vs. Firewalls (why vs. ?)
From: Chris Byrd <cbyrd01 () gmail com>
Date: Tue, 7 Feb 2006 18:04:37 -0600

Often you can find other indicators in otherwise protocol compliant
traffic based upon policy enforcement, such as length of the URI,
permitted user agents strings (before someone says it, yes it could
easily be spoofed - but it can't hurt to check), content length,
content type mismatches, etc.

Also, often traffic analysis can be your friend, or as Marcus Ranum
said it best, in his signature sang-froid manner, "The first law of
log analysis (and IDS) reads: The number of times an uninteresting
thing happens is an interesting thing."

If all else fails, a review of your DNS logs or signature-based IDS
can pick the rest out.

Then it's time to get out the LART.

On 2/4/06, Gabriele Buratti <gabriele.buratti () netasq com> wrote:
Dave Piscitello wrote:
 > If you take issue with this, consider
 > that some companies who bash proxies as being performance inhibitors
 > bolt SSL VPNs onto their firewalls.

Yep ! You still need proxies to do this SSL stuff as long as to hook an
antivirus for example.
Remember the old networking rule "switch when you can, route when you
must" ? In this field could be read as "analize on-the-fly when you can,
rewrite with a proxy when you must".
This is something more than "cutting the corners" this is using the best
tool available for each job.

 > Marcus J. Ranum wrote:
 > The fundamental issue always boils down to whether your product
 > inherently implements default permit or default deny; what it
 > does with the stuff that it will, inevitably, encounter that is
 > outside of its knowledgebase.

You have to use both approaches here: let's say our knowledgebase is the
definition of http protocol as it should be. So, if you find malformed
http (=non compliant) you drop it. What if you find some instant
messaging traffic (you don't want in your network) that is http compliant ?

        Gabriele



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