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: Thu, 7 May 2020 08:20:40 +0200

On 05/05/2020 21:44, Gert Doering wrote:

Hi,

On Tue, May 05, 2020 at 08:47:04PM +0200, Francois-Xavier Le Bail wrote:

So, given that the first 16 bits are "4 bit always 0, and 12 bits
reserved-must-be-set-to-0", using these as heuristics for "if two 0-bytes
are following the MPLS headers, it's a control word, so we skip 4 bytes
and the rest is a regular Ethernet packet" should work.

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).

Proposed patch attached.

With new '-T mplsethnocw' option to force 'Ethernet without Control Word' decode.
(from Francesco Fondelli comment)
-- 
Francois-Xavier

Attachment: print-mpls-2.patch
Description:

--- End Message ---

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