GoKawiilFrom Oscilloscope to Wireshark: A UDP Story
UDP is a transport-level protocol for sending messages through an IP network.
It sits at level 4 in the OSI model:
7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data link 1 Physical
Like many of you, I've got hardware on my desk that's sending UDP packets, and the time has come to take a closer look at them.
Most "low-level" networking tutorials will bottom out somewhere at "use tcpdump to see raw packets". We'll be starting a bit lower in the stack; specifically, here:
This is a high-speed active differential probe soldered to an Oxide Computer Company rack switch. We're going all the way down to the metal.
(Huge thanks to Eric for the careful soldering that made this possible!)
Looking at the signals on an oscilloscope, we see data zooming down the wires:
The rest of this post will take us from these raw voltage waveforms all the way to decoded UDP packets. Hold on tight, we're going from L1 all the way to L4.
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