Network Lights


I need some understanding when it comes networking.
when I plug a cat 5 cable into my computer, a light illuminates from the female jack.
exactly what does that signify.

to that end... my patch cable goes to my wall jack, which is fed from a switch , which is fed from another  switch, which is fed ( for internet ) by my router, which is fed by my cable modem.   which one of those devices or connections are causing my computer's sock to illuminate?
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It depends on the implementation, normally the light to the left signifies that a cable is inserted correctly (other signify that the card is connected to the network, network being the first other network device in the chain) and the light to the right signifies data being received or transmitted. Sometimes these lights are combined into one.

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Hi intelogent,

To clarify, you are asking why the LED is on/flashing when you plug in the network cable into your RJ45 Ethernet port on your computer?

Generally there are two LED lights on the RJ45 Ethernet port. The one to the left would be on, this means that a link is established. The LED to the right is two tone, amber and green. They generally flash to indicate the connection speed.

Mr TorturSystem EngineerCommented:
+1, I fully agree with DrAtomic.
The device causing your computer network card to illuminate is the last switch because it is the connection between this last switch and your computer (through your wall jack) for which we can say, if the light is on, the signal is on, and with the appropiate configuration this 2 devices can communicate trough network.

But this light on is about the physical link. You could have 2 computers with a network cable between them, lights on the newtork cards will be on but if they are not in the same ip range they will not communicate.

Don't know if it is clear for you, my english is far from perfect.
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andreasSystem AdminCommented:
The leds just indicate

1. the physical link between the 2 devices connected directly.
2. Activity on that network link. (Ethernet frames transmitted/received)

If does not indicate if you have internet connectivity or a working connection that is able to access somewhere.
It just shows the hardware link is ok and that/if there is any activity on that link.

If the LES are off, then its sure you do not have ny connectivity ofer that link.
intelogentAuthor Commented:

so then if I powered on  a switch , and then attached my patch cable, are we saying my port would illuminate?
and the same is true for the port on the switch. it too would illuminate if a LINK to a device is established?

how about a link between two switches, would that also illuminate both  ports?
andreasSystem AdminCommented:
Yes both ports of the link will illuminate, if both devices ports are active (e.g. devices are powered and NICs initialized).

For 2 switches its the same. if they are linked the leds will show it. Some Switches (usualy older ones) need uplink-Ports or crossover Cables to connect them, as they dont have Auto MDI-X support.
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