MDI is a standard twisted pair ethernet port (Medium Dependent Interface). A port labeled MDI/MDIX usually has a switch that will swap the transmit and receive pairs so that you wouldn't need a crossover cable (as required for a hub to hub connection). An Auto MDI/MDIX will automatically detect if a crossover is required and make the swap for you internally. The X in MDIX is short for crossover.
Sorry, I got carried away and forgot the first part: MDI-II is a "cascade" port for allowing two or more hubs to be connected together. Some brands of hubs will have two jacks or even DB-25 connectors on the back for cascading hubs - these are often proprietary for stack management and/or increased speed.
Reference: http://www.computing.net/answers/networking/mdiii-vs-auto-midmdix/10009.html
Sorry, I got carried away and forgot the first part: MDI-II is a "cascade" port for allowing two or more hubs to be connected together. Some brands of hubs will have two jacks or even DB-25 connectors on the back for cascading hubs - these are often proprietary for stack management and/or increased speed.
Reference: http://www.computing.net/answers/networking/mdiii-vs-auto-midmdix/10009.html
