I have a persistent issue with my machine which, although not a hindrance for the time being, worries me to the point of having to ask about it. Like most people I connect my desktop to the router via a short (2m) LAN cable; When the PC is on a green led on the router lights up to indicate that port is up and running as is the case for most routers.

What creeps me out is that whenever my computer is restarting or powered off, the router led for its port will sometimes flicker randomly. I don't mean blinking consistently to indicate something: It behaves like a flickering light bulb, staying on but flicking off for a moment at random intervals. This never happens while the machine is powered, only while it's rebooting (in POST) or shut down... when running its router led is always on without any flickering, internet always works perfectly fine too. Yesterday I could confirm the accompanying orange led in the LAN port of the motherboard flickers together with the router port when this happens. I tried plugging the cable into different ports on the router as well as using a new patch cable to connect the PC to it, all do the same thing.

I don't get why the router would see my computer while it's shut down anyway, considering I have wake-on-lan explicitly disabled in BIOS. But for instance: If my computer was on and I tell it to shut down, the router led will either do the blinking or remain disabled until I turn the machine back on... if however I cut power to the PSU then plug the power outlet back in but don't turn the computer on right away, the led will pop back on and act as if my computer is running: Why does the router randomly decide to see or ignore my computer when it's shut down, instead of always taking one action and not blinking at that? This randomness confuses me.

I primarily wish to know if this is reason for concern and others are seeing similar results with their hardware. Like I said the network works flawlessly when everything's powered on, I can move the cable around and reboot the router or do anything, the flickering only goes on when the computer is off. Mainly worried if this could indicate a hardware issue that may someday extend, if this isn't sign of a potential failure I don't care for the effect then.

Motherboard: ASUS PRIME X370-PRO: https://www.asus.com/us/motherboards...prime-x370-pro
Router: D-LINK DIR-842: https://eu.dlink.com/ro/ro/products/...gigabit-router

I don't think there's any reason to be concerned.

Just guessing what you notice is part of the existence of WOL, DHCP, Samba, NTLM & other network functionality. I have lots of PCs, and see lots of LAN port LED activity when I don't expect to see any. Some protocols are noisy, which creates traffic that lights LEDs. When WOL capability is present on a motherboard, I don't think the port is powered down until the PS is powered off and its capacitors are depleted, and correspondingly, if the PS has power, it's providing standby power available for starting up and WOL. Does your LAN port quiet down if DHCP for ethernet in the router is disabled? What besides your PC and router live on your LAN?

Thanks for clarifying, that sounds a lot more okay then. I believe I need DHCP enabled to get internet so I'd rather not mess with the settings, disabling the port would likely make the light go away though. I have wake-on-lan explicitly disabled in BIOS but I guess it still senses it for other reasons. If it's by design I don't mind, only making sure it's not a sign of the system not dealing with electrical currents the right way.

Your computer isn't really "off" until you either unplug it or if your power supply has a mechanical switch, you flip that.
https://en.wikipedia.org/wiki/Advanc...e#Power_states
If the computer is from just before the millennium or after (not AT, but ATX), your motherboard firmware is still active in "soft off" state doing ACPI and other stuff. Boards with AMT or other remote, "out of band" technology built-in can also be active in the "soft off" state.