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Re: HTTP Inspect and packet reassembly
From: Bhagya Bantwal <bbantwal () sourcefire com>
Date: Fri, 29 Oct 2010 10:34:23 -0400

On Thu, Oct 28, 2010 at 9:40 AM, L0rd Ch0de1m0rt
<l0rdch0de1m0rt () gmail com>wrote:

Hello.  I am investigating a situation where TCP streams are being
fragmented quite small at the IP layer for some reason (load
balancer?) and it seems to be causing problems for some of my rules
that leverage HTTP Inspect.  From the manual I read this:

"The current version of HTTP Inspect only handles stateless
processing. This means that HTTP Inspect looks for HTTP
fields on a packet-by-packet basis, and will be fooled if packets are
not reassembled. This works fine when there is
another module handling the reassembly, but there are limitations in
analyzing the protocol. Future versions will have
a stateful processing mode which will hook into various reassembly
modules."

OK, so HTTP Inspect is stateless and doesn't reassemble packets.  But
then there is the sentence, "This works fine when there is another
module handling the reassembly, but there are limitations in analyzing
the protocol."  So my question is, if I also have Stream5 enabled for
TCP, is that a sufficient "another module" or are there still
"limitations" with the HTTP protocol?


Yes. Stream5 reassembly is sufficient. It is suggested to turn on reassembly
on both HTTP server and client ports. Changes have been made to HTTP inspect
to inspect both stream inserted and reassembled packets.

-B


Specifically, I have problems with rules that use uricontent and
content and need to match across more than one packet.

Thanks!

-L0rd C.


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------------------------------------------------------------------------------
Nokia and AT&T present the 2010 Calling All Innovators-North America contest
Create new apps & games for the Nokia N8 for consumers in  U.S. and Canada
$10 million total in prizes - $4M cash, 500 devices, nearly $6M in marketing
Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store 
http://p.sf.net/sfu/nokia-dev2dev
_______________________________________________
Snort-devel mailing list
Snort-devel () lists sourceforge net
https://lists.sourceforge.net/lists/listinfo/snort-devel

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