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One flash, one packet? (programming.dev)
submitted 9 months ago by to c/networking@sh.itjust.works
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I've always wondered whether network interfaces that have these flashing lights flash as a gimmick or do they actually indicate the flow of traffic? Perhaps one flash per packet in or out? I wish I could remember what my call up modem looked like to make a historical comparison too.

TL-SG105E

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[–] [S] 3 points 9 months ago (4 children)

I went down some kind of a rabbit hole. I looked up my motherboard's NIC's data sheet and... Dam it! Why is tech so interesting!?

Source: https://datasheet4u.com/pdf-down/R/T/L/RTL8125BG-CG-Realtek.pdf

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  • [–] 2 points 9 months ago* (3 children)

    Something to be wary of when interpreting the datasheet:

    • Act10 = LED blinking when Ethernet packets transmitted/received at 10Mbps.
    • Act100 = ...
    • Act1000 = ...

    Bad wording on their part. What they really mean is: "LED blinking when Ethernet packets transmitted/received AND the link is currently in a XYZMbps link speed mode". The mode is negotiated once after you plug a cable in and usually does not change after that, regardless of how much data you try to send.

    Technically each linkspeed/mode is a whole ethernet standard of its own, but we mostly gloss over that and pretend to end users that they're backwards compatible.

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  • [–] [S] 1 point 9 months ago (2 children)

    Very insightful! Are those the speeds that I can cat from /sys/class/net/[interface name]/speed? Assuming you know Linux, that is. Those negotiated speeds, are they hardcoded into the NIC and selected/negotiated based on what category cable I'm using and other such hardware related factors? Also, is there any "wiggle room"? As in, does it do a speed test to check the limits of the physical layer or does it just follow some vendor specifications?

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