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Wireshark-users: Re: [Wireshark-users] RTP decoded as DPLAY in V1.0.0

From: "Keith French" <keithfrench@xxxxxxxxxxxxx>
Date: Fri, 11 Apr 2008 13:11:50 +0100
Jaap,

I have tried the UDP preference "Try heuristic sub-dissectors first", but didn't solve the problem. I always have the RTP preference "Try to decode RTP outside of conversations" ticked.

Has anything changed in the dissectors in Wireshark V1.0.0, because it was decoded as RTP fine in V0.99.8?

Keith.

----- Original Message ----- From: "Jaap Keuter" <jaap.keuter@xxxxxxxxx>
To: "Community support list for Wireshark" <wireshark-users@xxxxxxxxxxxxx>
Sent: Friday, April 11, 2008 10:26 AM
Subject: Re: [Wireshark-users] RTP decoded as DPLAY in V1.0.0


Hi,

This is really a conceptual problem. A port number is to be associated
with its service. That concept break when talking about dynamic data
ports, these are negotiated 'by other means'.

Wireshark tries to pick up these negotiations, like SDP, and configure the
dissectors accordingly.
Otherwise it tries to heuristically determine the protocol. That is the
case with the DirectPlay protocol, its not related to a specific port as
you state.

These methods aren't perfect. Therefor the dissectors are outfitted with
preferences to help make Wireshark make the right choices. In this case
the UDP preference "Try heuristic sub-dissectors first" might help, if
switched off. Another may be of the RTP dissector, "Try to decode RTP
outside of conversations".

Yet another option is to select the DirectPlay protocol in the packet
details pane and select "Disable protocol..." from the righthand click
menu. That knocks out the DirectPlay dissector for this session. Or you
can disable it completely from the Analyze|Enabled Protocols... menu
option.

Bottom line is: protocol usually give poor support for solid heuristics.
With more and more protocols being dissected in Wireshark these collisions
are bound to happen more often.

Thanx,
Jaap

Since Wireshark V1.0.0 (on Windows XP SP2) an RTP packet using UDP port
number 26642 is being decoded as DPLAY. This port number is in the range
used by Cisco for RTP. In V0.99.8 and before it has always been decoded as
RTP.

Obviously I can do a "Decode As" for the time being.

I assume this is a bug, and if so I will raise it on there when bugzilla
is back up again.

Keith French.

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