Packet Dissection Amarcord...


Back to packet dissection for troubleshooting…

Amarcord is a movie by Federico Fellini that mean “I remember”. Well, after a few years (some 20), I’m back looking at raw network-level captures from tcpdump to figure out what’s going on with some devices that seems to give bad answers.

On the other hand, it might be the client that is not able to understand those same answers. I’m more inclined to blame the server, though.

At a higher level, I had the joy of coding a quick client myself in Perl, sending the same request to the server and not getting an error. Which led me to think that the other client was to blame.

Alas, comparing the two real low-level requests, and the answers, got me back to my original thought: the server is probably to blame. This also seems to be supported by Wireshark’s internal dissector, which seems to point out that there’s extra stuff in the answer to the first client.

If you’re wondering, the two queries have some slight differences, which might actually trigger the wrong behaviour. I didn’t find anything around, though, which might mean bad web surfing skills, OR a decreased quality in queries to search engines.

NO, I didn’t ask ChatGPT.

Now I’m left with doing some manual low-level bitwise dissection of the packets, to find out where the truth lies. Which is something I was doing some 20+ years ago, leading to my minimal yet acknowledged contribution to the venerable Wireshark itself, yay!

Stay safe!

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