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Wireshark-bugs: [Wireshark-bugs] [Bug 3112] CDP Checksum Calculation Incorrect

Date: Sun, 4 Jan 2009 09:28:56 -0800 (PST)
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=3112





--- Comment #12 from Greg Neujahr <wireshark@xxxxxxxxxxxxxxxxxxxxx>  2009-01-04 09:28:55 PDT ---
(In reply to comment #11)
I can assure you the capture is geniune. I'll post another sample or two from a
cisco 800 series router as well as another capture from the same switch
(perhaps sourcing from a different port for varity).

I don't see any reason why it should have to be primed to -1, and don't think
such a thing would be neccessary (not mentioned in any documentation I can
find). The code I wrote to generate CDP packets initializes to 0x0000 for the
checksum, runs the code I provided, and then inserts that into the packet
(byteswapped). The switch accepts the generated CDP packets and processes them
normally. 

If you provide a patch to the current SVN before comitting it, I'll be glad to
test it with the switch here this evening to see if it validates against it.

Additionally, I'd like to offer my apologies for being a bit slow on this. My
schedule has been up in the air since before the holidays, and it's hard to
nail down time to work. It took me some time to get the dev environment working
to compile wireshark to test/debug these packets, so that was a small
hinderance as well. But, I have been working on making the packet produce a
valid checksum verification all morning, so provided you have a fix for it, I
will be happy to test for you.


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