Cisco ICND1 Flashcard: Copper Cable Pinouts for RJ-45

There are three types of copper cabling most concerning to Ethernet for the RJ-45 jacks: straight-through, cross-over, and roll-over. You can do a simple visual inspection to determine the pairing and type of cable it is. If you're constructing the cables to a custom length, you could use a special board with the input pins and output pins labelled 1 to 8 and they light up as you decide which order you want them in as you clip on the head. Click!

RJ-45 jacks for Ethernet, also used for ISDN BRI
(Deconflict DB-60 used for connecting synchronous serial interfaces and Cisco routers, configuring WAN links and T1, E1 high speed lines)

RJ-11 jacks for telephone

RJ-48 connectors on CSU/DSU WAN interface EIA-TIA 232 at the customer end.

Cabling

An insulating material covers each individual copper wire in the UTP cable; the wires wrap around each other (twisted pair). They are subject to electromagnetic interference.

Straight Through, UTP (unshielded twisted pair)
Pins 1,2,3 and 6 used
Pin 1 to 1, 2 to 2, 3 to 3, 6 to 6
Best to have the other unused pairs match up too.
Hubs or switches provide the "twist" to match TX to RX
Connects devices at the different layers of the OSI model, ie. Server to Switch

Cross Over
Pins 1,2,3 and 6 used
Pin 1 to 3, 3 to 1
Pin 2 to 6, 6 to 2
Connects devices at the same layer of the OSI model, ie. Router to Router

Roll Over
Used for connecting the console port on router to computer.
Cable is rolled, simply reverse the pins
Pin 1 to 8, 2 to 7, 3 to 6, 4 to 5, 5 to 4, 6 to 3, 7 to 2, 8 to 1
The console port is used for local access to the router, when physical access is required, like for password recovery.


Another way of looking at the pinouts.
Straight Through
sender     receiver
1               1
2               2
receiver   sender
3              3
6              6

Cross Over
sender      receiver
1               3
2               6
receiver   sender
3              1
6              2