Ethernet cables are used to connect devices together in a local area network (LAN). There are different types of Ethernet cables, with the most common being straight-through and crossover cables. Crossover cables are used for connecting similar devices together, like connecting two routers or two computers directly. The wiring inside a crossover cable is crossed over, allowing the transmit pins on one device to connect to the receive pins on the other device. This crossing over of signals allows the two devices to communicate.
Pinout of Ethernet Cables
Ethernet cables use RJ45 connectors that have 8 pins. The pins are numbered 1 through 8. Here is the typical pinout for a straight-through Ethernet cable:
| Pin | Color | Signal |
|---|---|---|
| 1 | Orange/White | Transmit+ |
| 2 | Orange | Transmit- |
| 3 | Green/White | Receive+ |
| 4 | Blue | Unused |
| 5 | Blue/White | Unused |
| 6 | Green | Receive- |
| 7 | Brown/White | Unused |
| 8 | Brown | Unused |
As you can see, pins 1 and 2 are used for transmitting data, pins 3 and 6 are used for receiving data, and pins 4, 5, 7, and 8 are unused. The transmit pins on one end connect straight through to the receive pins on the other end.
Now here is the pinout for a crossover Ethernet cable:
| Pin | Color | Signal |
|---|---|---|
| 1 | Orange/White | Receive+ |
| 2 | Orange | Receive- |
| 3 | Green/White | Transmit+ |
| 4 | Blue | Unused |
| 5 | Blue/White | Unused |
| 6 | Green | Transmit- |
| 7 | Brown/White | Unused |
| 8 | Brown | Unused |
Notice how the transmit and receive pairs are crossed over – pins 1 and 2 now connect to the receive pins (3 and 6) on the other end. This crossover is what allows similar devices like routers and computers to communicate.
The Color of Pin 3
To answer the original question – what is the color of pin 3 in a crossover cable?
Looking at the pinout table above, we can see that pin 3 uses the Green/White colored wires.
So the color of pin 3 in a crossover Ethernet cable is Green/White.
This crossover wiring is essential for connecting like devices. If two computers or two routers were connected with a straight-through cable, the transmit pins would be connected to the transmit pins on the other end. This configuration doesn’t allow for proper communication, since both devices would just be transmitting data simultaneously.
The crossover pinout flips the transmit and receive pairs, enabling each device to send and receive data properly. This is why crossover cables are required for linking up identical devices.
Uses of Crossover Cables
Some of the most common uses of crossover Ethernet cables are:
- Connecting two routers or switches together
- Connecting two computers directly for file transfer
- Connecting a router to a computer or server’s uplink port
- Connecting other networking devices like hubs or modems
- Testing Ethernet ports during troubleshooting
Routers and switches often have uplink ports specifically designed for crossover cables. On many routers, one of the LAN ports can also function as an uplink port when needed. This allows easy connection to another device without a crossover cable.
For computers and servers without uplink ports, a crossover cable is required for direct links. The auto MDI/MDI-X feature found on some NICs (Network Interface Controllers) can automatically adjust for straight-through or crossover cables. But for hardware without this, crossover cables are a must.
The direct router-to-router and computer-to-computer connections made possible by crossover cables are essential for installing and configuring networks. Crossover cables enable admins to link devices together temporarily for management, troubleshooting, migrations, and more.
How to Wire Ethernet Crossover Cables
Constructing custom crossover cables is useful for many IT professionals. Here are the basic steps to wire your own:
- Obtain a length of Ethernet cable and RJ45 connectors.
- Use the crossover pinout to determine which wires cross over from the T568A or T568B standards.
- Trim and organize the cable wires so the correct wires match up to pins 1-8.
- Insert the wires fully into the RJ45 connector following the crossover pinout.
- Crimp the connector firmly using a crimping tool to hold the wires in place.
- Test the assembled cable to verify a proper crossover connection.
It’s important to carefully follow the proper crossover pinout. One wiring mistake can prevent the cable from functioning. Testing the cable is a must once it’s crimped together.
Many Ethernet cables also have wires colored according to the 568A or 568B standards. It’s important not to confuse these with the crossover pinout colors. The crossover pairs will seem reversed from what 568A/B dictates.
Summary
To summarize the key points:
- Crossover Ethernet cables cross the transmit and receive wire pairs, allowing direct device-to-device connections.
- Pin 3 on a crossover cable uses the Green/White wires.
- Crossover cables are essential for connecting routers, switches, servers, and other networking equipment.
- Properly wiring a crossover cable requires following the correct crossover pinout.
So in a crossover Ethernet cable, pin 3 will always be the Green/White colored pair. This crossover wiring enables two similar devices to communicate effectively. While straight through cables are more common for basic connections, crossover cables still play an important role in LAN administration and troubleshooting.
Conclusion
The color of pin 3 in a crossover Ethernet cable is always Green/White. This wiring allows devices like computers and routers to transmit data to each other properly. Crossover cables join the transmit pins on one end to the receive pins on the other, enabling direct communication not possible with straight-through cabling. Understanding crossover pinouts and wiring is an important networking skill for effective LAN management. With the right cabling, admins can link up devices, troubleshoot problems, and keep their networks humming along smoothly.
