[General] What is Auto-negotiation?

Auto-negotiation is a technology standard defined by IEEE802.3u. According to this standard, auto-negotiation in a 100Base-T working group is a mechanism that takes control of the cable when a connection is established to a network device. Auto-negotiation detects the various modes that exist in the device on the other end of the wire and advertises its own abilities to automatically configure the highest performance mode of interoperation. Auto-negotiation defines 4 modes: 10Base-T half duplex, 10Base-T full duplex, 100Base-TX half duplex, and 100Base-TX full duplex. It automatically switches to the correct mode while a common mode with the highest performance is determined. Auto-negotiation passes control of the cable to the appropriate technology and becomes transparent until the connection is broken.