What is Auto-MDIX

Auto-MDIX (automatic medium-dependent interface crossover) is a computer networking technology that automatically detects the required cable connection type (straight-through or crossover) and configures the connection appropriately, thereby removing 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”. Auto-MDIX was developed by HP engineers Dan Dove and Bruce Melvin.

Auto-MDIX was spawned one day when Melvin was frustrated while looking for a cross-over cable in the lab, and asked Dove to invent a solution. His inspiration led Dan to develop the method which utilizes a pseudo-random number generator to decide whether or not a network port will attach its transmitter, or its receiver to each of the twisted pairs used to Auto-Negotiate the link.

Subsequently, Dan went on to promote Auto-MDIX within the IEEE-802.3ab (1000BASE-T) standard and also develop patented algorithms for “Forced Mode Auto-MDIX” which allows a link to be automatically established even if the port does not auto-negotiate.

However, ease of use may have its drawbacks as users might (by mistake or on purpose) connect two Auto-MDIX switch ports to each other, causing a switching loop.