Don't take it for granted: the use of crossover and direct connections,

Anyone who has learned about the network knows that cross lines must be used to connect to the same level-1 network device. ---- DP

But now it seems that no one has done this. The two computers are connected by a direct connection, and some people think that the direct connection is justified. In fact, we can now use a direct connection to connect to the same level of equipment (for example, two PCs). Currently, most network adapters include a feature called "automatic network cable line sequence recognition, this feature is the first in HP. This function is determined by the Physical Layer Chip. Only when the NIC supports this function can two PCs be connected through a direct connection. Otherwise, there are still many network devices that do not support this function.

Let's take a look at what is said on the Wiki:

Auto-mdix

Auto-mdix, which stands for automatic medium-dependent interface crossover, is a computer networking technology developed by HP. it automatically detects the required cable connection type (straight-through or crossover) and configures the connection appropriately, thereby obviating the need for crossover cables to interconnect switches or Connecting PCs peer-to-peer. when it is enabled, either type of cable can be used and the interface automatically corrects any incorrect cabling. for auto-mdix to operate correctly, the speed on the interface and Duplex Setting must be set to "Auto ".

Summary

Using Local Area Network (LAN) products use a medium consisting of twisted pair copper wire pairs for the transmission and conflict of data. it is generally a requirement that one or more pairs be used for transmission of data in one direction and one or more other pairs to receive data in the opposite direction. the connection between two node devices is a link. using LAN devices, which employ a full-duplex medium, have different pairs for transmission than for conflict and require, therefore, that each end of the link use a defined assignment for its twisted pair connector to a particle pair of wires. if the transmit pair of wires of one device is connected to the transmit connectors of another, obviously the communication link will fail.

Most LAN standards address this problem by assigning different Connector pins to the wires in the twisted pair at the RJ-45, which is often referred to as the media dependent interface (MDI ). in switched networks, network interface devices (NIC) may be directly connected to another Nic, or a repeater may be connected to another repeater, or a repeater may alternately be connected to a switch. depending upon the assignment of pins in the network interface, it is sometimes necessary to use a crossover cable to address the problem that both products use the same pin designations on their interfaces. determining whether the interface requires this cable can cause confusion and frustration if the customer lacks the necessary cable.

To get around this problem, some products use a manual "mdix" switch. but that still requires user intervention. the need arose, then, for automatically ensuring viable connections among MDIs in complex LANs. HP's auto-mdix technology upgrade tively solves the problem of lock step interaction among devices having MDIs from various well-known manufacturers

Http://en.wikipedia.org/wiki/Auto-MDIX

Http://www.hp.com/hpinfo/abouthp/iplicensing/automdix.html