Ethereal-dev: Re: [Ethereal-dev] 2 patches to packet-gtp.c

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From: Trauer Andreas <andreas.trauer@xxxxxxxxxxx>
Date: Tue, 12 Nov 2002 12:18:21 +0100
> Guy Harris wrote:
> > (Another possibility would be to have the GTP dissector have its own
> > dissector table, and have only the configuration protocols for PPP
> > register in that table, so bogus protocol ID values don't 
> > cause us to
> > dissect "configuration options" as IP packets or something such as
> > that.)
> 
Andreas Trauer wrote:
> I wouldn't do that. The standard leaves a small path: "The support of 
> other protocol identifiers is implementation dependent". So 
> if the field
> says the following data are IP (0x0021), not IPCP (0x8021), 
> then I would
> give it a try to decode it that way. Of course it doesn't 
> make sense, but 
> test tools could send such nonsense to challenge the unit under test. 
> It is nicer to have that nonsense decoded correctly ;-)

Another possiblity is to give an additional warning before decoding if 
the MSB of the protocol field is zero, but the value is found in the
dissector table.