Wireshark-dev: [Wireshark-dev] SIP heuristics
From: Lars Roland <[email protected]>
Date: Thu, 08 Jun 2006 22:31:25 +0200
//Hello Jaap,

I just subscribed to this list and discoverd your mail in the archive.

The request line starts with the Method. Anything before is not SIP and shouldn't be marked as such.
Q: Should the heuristics try to discover SIP Packets encapsulated within 
unknown data?
IMO it should only discover SIP Packets, when the tvbuff in question 
directly starts with a SIP header and contains no unknown leading bytes.
The problem here is, that the Request Line starts with the Method, which 
can contain a lot of different ASCII characters. A heuristic, which 
detects a SIP Request Line 100% correctly can be very time consuming, 
because of the complex charset
As you noticed the SIP heuristics are too weak at the moment. IMO we 
should have strong heuristics, which may not detect all syntactically 
valid SIP packets, but will never detect false positives. Perhaps we 
should limit the heuristic detection to known SIP methods.
Best regards,

From// Jaap Keuter <[email protected] <mailto:[email protected]>> //Date// Wed, 7 Jun 2006 15:32:25 +0200 (CEST)


Now that the dust is settling (until the user community comes barging in
;) let us slowly get back to the real stuff.

I've got trouble with SIP heuristics. Currently it tries to see if the
packet contains what looks like a few tokens, which are checked to certain
criteria. The trouble is that I've got SIP lines packed up in other
(binary coded) protocols, which do contain NULL characters. Still the SIP
heuristics take that as being part of the request line...... That can't be
right, can it? Shouldn't the heuristics take the UDP/TCP payload and take
the _zero terminated_ string in there to determine if it is a SIP packet
after all?

Your thoughts please,