Re: decode MPLS-contained packets?

[Francois-Xavier Le Bail via tcpdump-workers <tcpdump-workers () lists tcpdump org>]

> --- Begin Message ---
>
>
> From: Francois-Xavier Le Bail <devel.fx.lebail () orange fr>
>
> Date: Tue, 5 May 2020 22:03:00 +0200
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> On 05/05/2020 21:44, Gert Doering wrote:
> > > We should print "PW Ethernet Control Word" and the "Sequence Number", 2 last 2 octets of the 4.
> > > Like:
> > > PW Ethernet Control Word, Sequence Number xxx
> > I think we should only print this if "-v" is given.  Most of the time, 
> > both control word and sequence number are of little interest.
> >
> > I really like tcpdump's very compact "only the most relevant info" output
> > format (by default).
>
> OK for "-v" only print.
>
> Other information from Francesco Fondelli:
>
> -----------------------------------------------------------------------
> it is a bit more complicated than that, look for
>
>     /*
>      * No, there isn't, so use the 1st nibble logic (see BCP 4928,
>      * RFC 4385 and 5586).
>      */
>
> in
> https://code.wireshark.org/review/gitweb?p=wireshark.git;a=blob;f=epan/dissectors/packet-mpls.c;h=4ecb10d1216077b92e6d4ca2520340cf053414f4;hb=HEAD
>
> and also the PW ETH heuristic in looks_like_plain_eth
>
> https://code.wireshark.org/review/gitweb?p=wireshark.git;a=blob;f=epan/dissectors/packet-pw-eth.c;h=aec7b662d38ddb36514ed3c213df47ad53ad610b;hb=HEAD
>
> Wireshark MPLS heuristic is not perfect and has been criticized but is still there :-) hopefully
> correctly parsing your data as well.
>
> For tcpdump maybe a -T based approach is better?
>
> -T mpls (+ 1st nibble logic for IPv4/IPv6)
> -T ethpw
> -T ethpwnocw
> ...
> -----------------------------------------------------------------------
>
> Probably some more work to do...
>
> And probably linked to https://tools.ietf.org/html/rfc8469.
>
> -- 
> Francois-Xavier
>
> --- End Message ---
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