Network card LED is on, but the solution of the net display unplugged

Today encountered a dual network card work, a computer boss plug two card, a used to connect the outside network, a b connected to a lot of sub-computers, computer boss with a server like.

problem : that is, connected to the network network card a display no problem, the computer boss display is connected and can surf the internet, and another NIC B is not always smooth communication with the sub-computer, the error code shows that the network is not stable, and the computer NIC B indicator yellow light is normal, green light red light, The computer shows that this NIC B network cable is unplugged. Even if a, B network card Interchange network cable Connection, that is, B connected outside the network, a even sub-computer, B network card also does not, the light is normal (there is data communication AH) but the computer shows that the cable has been pulled out.

For a dual-NIC computer is also, as long as the connection of the sub-computer network cable plug, even if the indicator light allbright (yellow, green flashing flash), the computer will still show that has been unplugged.

workaround : After ensuring that the network is not a problem, and the IP, gateway and other configuration are correct, modify the NIC B (connecting the sub-computer) network card properties of "speed and duplex", such as:

Click "Configure"-Select "Advanced"-select "Speed and Duplex"-Tap the yellow circle drop-down box and select one of the options

I chose 100Mbps half-duplex.

Why do we have to choose this? Professionals say that is the network problem or the switch problem (I have not figured out), I thought it is the network card has a physical fault, the professional said the network card if there is no lightning strikes and other bad situation is generally not bad.

Hope to help everyone, is also a summary of my today:)

Network card LED is on, but the solution of the net display unplugged