Wireshark-bugs: [Wireshark-bugs] [Bug 3112] CDP Checksum Calculation Incorrect
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From: bugzilla-daemon@xxxxxxxxxxxxx
Date: Sun, 4 Jan 2009 04:55:14 -0800 (PST)
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=3112





--- Comment #11 from Jaap Keuter <jaap.keuter@xxxxxxxxx>  2009-01-04 04:55:13 PDT ---
I'm starting to doubt the example CDP packet supplied for this bugreport. There
is no way I can get the same result when calculating the checksum, other than
initializing the sum to -1, and using byteswap. I've found 4 other CDP captures
at http://packetlife.net/captures/protocol/cdp/ , some with odd length, and the
byteswap made the checksum work with in_cksum(). There was no need to prime the
sum with -1 to make the results match, so that leads me to believe that
byteswap is all that it takes. This also matched the remark in the code of
cdp-tools (see http://gpl.internetconnection.net/)

I'm working on a patch to implement this change, and plan to commit it in the
near future.


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