networking basic question

[Chakravarthi]

Hi,

why do you need to use RJ-45 cross-over cable between two swithches and why you need to use straight RJ45 cable between PC-switch.

regards
chakri

[Les Ligetfalvy · Accepted solution]

MDI ports have the receive and transmit on different pins than MDI-X. End devices use an MDI pinout and expect to connect to a hub or switch which use MDI-X. If end devices were the same as switches, you would have to use crossover cables for them but this way you only need them for hub to hub connections.

BTW, most newer switches and hubs now have Auto-MDI meaning that they will do the crossover internally negating the need for crossover cables. Also be advised that gig ethernet uses all the pairs.

See the pinouts for 10/100 at http://www.cabletron.com/support/techtips/tk0231-9.html but you should be able to google for a better answer than I can provide.