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Investigating an "evil" RJ45 dongle

(lcamtuf.substack.com)
289 points zdw | 1 comments | 17 Jan 25 20:41 UTC | HN request time: 0s | source
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baq ◴[17 Jan 25 20:53 UTC] No.42743115[source]▶
RJ45 nazi here: these should be called 8P8C

I’ll show myself out

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leptons ◴[17 Jan 25 21:27 UTC] No.42743463[source]▶
TIL. After maybe 25 years of using this connector, I've never heard it called 8P8C. I knew Ethernet has used other physical layers including coax, which I used to run between Amigas way back in the day. But, today I finally learned about 8P8C.
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SAI_Peregrinus ◴[17 Jan 25 22:07 UTC] No.42743794[source]▶
RJ45 isn't even actually the same connector, at least not in the original FCC naming. That was an 8P8C keyed modular connector. RJ45 connectors had only two of the positions connected to wires (one phone line) an internal resistor between two of the other positions, and a keying bar that stuck out of the plug so they wouldn't even go into the unkeyed 8P8C jacks we use for Ethernet.

So I'll still call them RJ45 connectors. Because nobody has time to say "8P8C unkeyed modular connector" every time!

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necovek ◴[17 Jan 25 22:16 UTC] No.42743854[source]▶
Weren't phone lines something like RJ11 or RJ12?

FWIW, TIL about 8P8C.

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1. SAI_Peregrinus ◴[18 Jan 25 00:41 UTC] No.42744733[source]▶
Yes, and RJ45. It used to be defined by the US FCC[1] in 47 CFR Part 68 Subpart F. Along with others, like RJ31X, RJ38, etc. The "RJxxy" numbers were the Universal Service Order Codes (USOCs), the `y` value described the use (e.g. W for wall-mounted jacks). Pages 143 & 144 of the PDF (403 & 404 of the print version) have the electrical connection diagram and the USOCs, pages 125-129 (385 -389 print) have the mechanical drawings. The unkeyed 8p8c connector we use today is also in there (pdf pgs 103-113), but the RJ45 series used the keyed connector! It's RJ31X & RJ38X that used the unkeyed 8-position series jack & 8-position plug we call RJ45 today (pdf pages 137-138).

[1] https://web.archive.org/web/20170705131407/http://www.tscm.c...