MDI-X in cisco switch

[nnn_sss22]

Hello

Please tell me something about MDI-X.

by default switch perform function full duplex. Please tell me on which case we set half duplex port? and on which case we decrease the port speed? thanks

Regards 

[Julio E. Moisa]

Hi

MDIX is a feature to allow use straight copper cable between switches, it is no more configurable on the new models. Before if you connect 2 switches directly you should connect them using crossover cable (always copper cable but with different sequence on 1 end). The new models can support straight cable connection between them by default.

Crossover cable, one end is straight and the other end has different color sequence. Image: Crossover

This link can be useful:

http://johan-eko.blogspot.com/2012/01/auto-mdix-using-cross-or-straigth-cable.html

:-)

[jwdoherty]

You're mixing apples with oranges when discussing MDI and duplex.

MDI/MDI-X is how the port's pins are assigned/connected, for example which pin is TX and which RX.  This to insure one side's TX pin connects to the other side's RX pin.

Correct pin connections are obtained by either reversing some connections in the cable or one of the ports.

Traditionally, to connect "like" ports, you needed a "cross over" cable. To connect "different" port you needed a "straight through" cable.  Also traditionally, most hosts ports are wired one way and hub/switch ports the other way so you could use "straight through" cables.

Modern switches often support auto-MDI, where the device's port's pins will detect what's needed to work.  However, such often depends on the port being in auto-negotiation mode.