My question is related to creating an unidirectional network cable.
I used these tutorials:
In principle it works by cutting a Category-5 cable in half, connecting the transmit pair (pins 1 and 2) of the sending side to the receive pair of the receiver side (pins 3 and 6), but you also have to connect pins 3 and 6 of the sending side to your bundle, creating some kind of loopback on the sender side. So in the end you have a point where three cables are connected and the link is working fine (you can send data in one direction etc.). If you do not create this loopback it does not work and the link does not come up on the sender side (on the receiver side it does!).
My question is: Why is that the case? Why can't I just connect the TX and RX wires of sender and receiver?
My guess is that it is related to the link pulses used for autonegotiation. My hope was that these are not present if I disable autonegotiation, which I did successfully with ethtool. (I also set the speed to 100 mbps and duplex to full.)
Yet the link still does not come up. So there must be more to that. Maybe there is also some way to tell the sender side that the link it is up. But I don't know if the link status is handled by the driver or directly by the chip (AX88772B).