Wireshark-dev: Re: [Wireshark-dev] Parallel Redundancy Protocol (PRP) dissector
From: Jeff Morriss <[email protected]>
Date: Mon, 16 Apr 2007 17:53:19 +0800
Hi list,

What do you think--how should we go about this?


Glattfelder Christoph (glc) wrote:
Hello Jeff

Unfortunately, a frame must be searched for the trailer to recognize it as PRP frame. But I see no problem to have it disabled by default.
Best regards

Christoph Glattfelder

Zürcher Hochschule Winterthur
Institute of Embedded Systems - InES

Technikumstrasse 9
Postfach 805
CH-8401 Winterthur
Tel. +41(0)52 260 69 74

[email protected]

-----Ursprüngliche Nachricht-----
Von: Jeff Morriss [mailto:[email protected]] Gesendet: Montag, 16. April 2007 10:26
An: Developer support list for Wireshark; Glattfelder Christoph (glc)
Betreff: Re: [Wireshark-dev] Parallel Redundancy Protocol (PRP) dissector

Meier Sven (msv) wrote:
This is a dissector for the Parallel Redundancy Protocol (PRP) defined in chapter 6 of the IEC 62439.
PRP uses two independent networks in parallel and allows redundancy 
without switchovers.
The protocol is sending Mac multicast messages with Ethertype 0x88fb. In 
addition to that it adds to every Ethernet frame a 4 byte trailer before 
the FCS. The trailer is detected by checking a size field and an 
identifier which are part of the trailer. Therefore, if the last 4 bytes 
of a frame match a correct trailer they get interpreted as a trailer, 
although it was probably not a real one.
Is there some way to know if the trailer is going to be there without 
searching for it?  As it is, registered as a postdissector (didn't even 
know those existed until now), this dissector will get called for every 
frame--which seems a bit excessive to me.
If there's no way to know ahead of time, maybe this dissector should be 
disabled by default, though I'm not sure how to best go about doing that.