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Router ports ( LAN wire ) & flashlights

bobbobbob

Member
Aug 31, 2016
51
1
41
I have TL-WR841N router.
+- 1 light is dedicated, if router receives electric support.
+- 1 light is dedicated, if router is connected to POE wire.

If LAN wire is connected to router and 1 device ( once turned on ) -> the one extra green square light will keep flashing.

If 4 ports have 4 LAN wires plugged, and those 4 LAN wires is plugged to computers, whos turned on, then -> extra 4 green lights will flash.


Question is: how router actually knows ( recognizes ) if computer is turned on. Because if computer is not turned on -> green light will not flash.
 

VirtualLarry

Lifer
Aug 25, 2001
45,459
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Well, traditionally, at least, not sure about that particular router and its POE capabilities, but generally-speaking, ethernet ports with LEDs on the jack, show a "link" and an "activity" LED. The "link" LED lights if the ethernet has a physical link (up), and the "activity" blinks when there is data transmitted or received on that port. I don't know of those LEDs are under hardware control, or BIOS/driver control, in which case they could be surpressed or hacked.

Edit: There may also be mobo BIOS options for disabling the LEDs. That would apply only to the end of the connection that the PC is connected to, and not the switch / router that it was plugged into, in that case, that device would have its own LED options.
 
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Mr Evil

Senior member
Jul 24, 2015
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mrevil.asvachin.eu
When something is connected to a port, it will periodically send a signal down the wire, even if there's no network activity. That allows the router (or whatever happens to be on the other end of the cable) to detect that something is physically connected. The computer can't send those signals if it's not turned on, thus the router doesn't detect it when it's off.
 

mxnerd

Diamond Member
Jul 6, 2007
4,693
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The same guy who wants to isolate all Wi-Fi signals and still able to use his computer/laptop? Now asking why the LED lights will turn on when computers are connected to the router?

Apparently he doesn't know what electricity is.
 

Mr Evil

Senior member
Jul 24, 2015
407
138
116
mrevil.asvachin.eu
The same guy who wants to isolate all Wi-Fi signals and still able to use his computer/laptop? Now asking why the LED lights will turn on when computers are connected to the router?

Apparently he doesn't know what electricity is.
Regardless of bobbobbob's posting history, I don't think the answer to this question is as abvious as it might seem. There are many ways to detect a connection, from simple mechanical switches often see with ¼" jacks, to measuring the reflection from an impedance mismatch. It also might not be obvious that network adapters can be initialized by the BIOS before the OS has loaded, and even connect to the internet at that stage.
 

JackMDS

Elite Member
Super Moderator
Oct 25, 1999
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I want to remind us ATX/mATX PSU

If a computer connected to the Electrical outlet, the computer can be off but the wired LAN card is partially alive. It is a feature that enables us to use Wake On LAN.

So if a computer with such wired LAN is plugged to a Net Switch the light is On even if the computer is Off.


:cool:
 

lexco

Member
May 9, 2013
28
0
66
I have TL-WR841N router.

+- 1 light is dedicated, if router receives electric support.

+- 1 light is dedicated, if router is connected to POE wire.

If LAN wire is connected to router and 1 device ( once turned on ) -> the one extra green square light will keep flashing.

If 4 ports have 4 LAN wires plugged, and those 4 LAN wires is plugged to computers, whos turned on, then -> extra 4 green lights will flash. I have checked the usage of transport layer protocols on the network, everything seems fine. Here you can check how the protocol works with Windows computers. All web domains redirect properly.


Question is: how router actually knows ( recognizes ) if computer is turned on. Because if computer is not turned on -> green light will not flash.
If one PC connected to the router is on, it will be added to the routing table automatically. So router knows the presence of the computer.
 
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bobbobbob

Member
Aug 31, 2016
51
1
41
The same guy who wants to isolate all Wi-Fi signals and still able to use his computer/laptop? Now asking why the LED lights will turn on when computers are connected to the router?

Apparently he doesn't know what electricity is.
I am.
[ Since later spring -> until early autumn ] I am using computer in the forest nowadays ( few kilometres from the house ).

Housemate is mad.

 

UsandThem

Elite Member
Super Moderator
May 4, 2000
11,459
1,970
136
I am.
[ Since later spring -> until early autumn ] I am using computer in the forest nowadays ( few kilometres from the house ).

Housemate is mad.
I bet they are mad. They apparently had a lot of fun sending EMI signals, and installing spying chips on your motherboard, and now you have taken that all away from them.

I bet they will soon discover your forest location, and hit you with a trojan virus beam-formed to your computer.
 

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