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

Date: Tue, 6 Jan 2009 02:00:54 -0800 (PST)
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=3112





--- Comment #36 from Jim Young <jyoung@xxxxxxx>  2009-01-06 02:00:49 PDT ---
Created an attachment (id=2645)
 --> (https://bugs.wireshark.org/bugzilla/attachment.cgi?id=2645)
Report generated from a modified version of cksumtest3

I've attached a slightly annotated report (the lines that begin with "#"). 
This report was generated from a modified version of the cksumtest3.c program. 
I modified the program to loop across 12 sets of my own CDP data.

If the "IOS CDP checksum" line is to be believed, it looks like all 12 of my
CDP packets check out as OK!

FWIW: I went searching for "historic" CDP packets in some older tracefiles. 
Interestingly I found many occurences of odd sized CDP packets where Wireshark
identified the cksum as "good".  But I also found plenty of "bad" cksums too. 

Curiously I also found what initially looked like some "bad" even length CDP
packets as well.  But it turns out these packets just happened to have very
short CDP payloads (just 23 bytes);  The frame got padded to 64 bytes!  One of
these short CDP packets was used in "Test D" in the attached report.


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