MDI

Stands for "Medium Dependent Interface." MDI is a type of Ethernet port found on network devices. It is often used in contrast with MDIX (or "MDI-X"), which is similar to MDI, but switches the transmit and receive pins within the interface.

When connecting two devices with an Ethernet cable, it is important that the transmit pins on one end line up with the receive pins on the other. If you connect a device with an MDI port to a device with an MDIX port, a standard straight through Ethernet cable will do the job. However, when connecting two devices with MDI ports, such as two computers, an Ethernet crossover cable is required. The crossover cable switches the send and receive ports on the two connectors, allowing data to flow correctly between two MDI or MDIX ports.

Straight-through and crossover Ethernet cables may look identical, but you can tell the difference by looking at the colors of the wires on each end. In a straight-through Ethernet cable, the colors will be the same on both ends, while in a crossover cable, the colors will be arranged differently.

On some network devices, the ports are labeled MDI or MDIX to help you choose the right type of cable. Routers often have multiple MDIX ports and a single MDI port called an "uplink" port designed to connect a device such as a cable modem. If you connect a device to the wrong port or use the wrong cable, it may not be able to communicate with the router.

Fortunately, Hewlett Packard developed a technology called Auto-MDIX (or "MDI/MDIX Auto Cross") that automatically switches between MDI and MDIX as needed. Today, most 10Base-T and 100Base-T network devices have Auto-MDIX ports, so it does not matter if you connect other devices using straight through or crossover cables. Additionally, Giagbit Ethernet (1000-BaseT) does not define specific send/receive pins, so it is not necessary to identify MDI or MDIX ports when connecting two Gigabit Ethernet devices.

Updated April 2, 2014

Definitions by TechTerms.com

The definition of MDI on this page is an original TechTerms.com definition. If you would like to reference this page or cite this definition, you can use the green citation links above.

The goal of TechTerms.com is to explain computer terminology in a way that is easy to understand. We strive for simplicity and accuracy with every definition we publish. If you have feedback about the MDI definition or would like to suggest a new technical term, please contact us.

Want to learn more tech terms? Subscribe to the daily or weekly newsletter and get featured terms and quizzes delivered to your inbox.

Sign up for the free TechTerms Newsletter

How often would you like to receive an email?

You can unsubscribe or change your frequency setting at any time using the links available in each email.

Questions? Please contact us.