Re: decode MPLS-contained packets?

[Gert Doering via tcpdump-workers <tcpdump-workers () lists tcpdump org>]

> --- Begin Message ---
>
>
> From: Gert Doering <gert () greenie muc de>
>
> Date: Thu, 7 May 2020 11:22:54 +0200
>
> Hi,
>
> On Thu, May 07, 2020 at 01:05:19AM -0700, Guy Harris wrote:
> > A mechanism where you could do something such as "-T tcp:1073:{protocol}"
> > to force traffic to TCP port 1073 to be dissected as the specified
> > protocol might be useful; in this case, we'd do something such as
> > "-T mpls:{protocol}" to force *all* MPLS packets to be dissected
> > as the specified protocol, and "-T mpls:{label}:{protocol}", to
> > force packets with a particular label to be dissected as the specified
> > protocol (which might mean you'd have to run tcpdump twice - once
> > to see what the label is, and once to decode the label.
>
> I find this to be a fairly complex solution, at least for my use case.  
>
> I know what I'm looking at ("tcpdump -s0 'label 12003'"), it's just 
> tcpdump not knowing what these packets are - so for these simple cases, a 
>
>   "-T mplsnocweth"
>   "-T mplscweth"
>
> (or whatever it's called in the end) would be sufficient.  The documentation 
> would need updating to make clear what happens behind the scenes ("this 
> forces some of the dissectors to decode the packet in a particular way", 
> and then possibly explain for each -T value to what sort of packets it applies)
>
>
> OTOH, as a long-term road map, why not :-)
>
> gert
>
> -- 
> "If was one thing all people took for granted, was conviction that if you 
>  feed honest figures into a computer, honest figures come out. Never doubted 
>  it myself till I met a computer with a sense of humor."
>                              Robert A. Heinlein, The Moon is a Harsh Mistress
>
> Gert Doering - Munich, Germany                             gert () greenie muc de
>
> --- End Message ---
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