Copper Cabling

Copper cabling is the primary medium employed in Ethernet networks. Its main role is to carry electrical signals that represent data.

You’ve likely seen this type of cable. It may be in your company’s network or at home, connected to your router.

Figure 1 – Copper Ethernet Cable with RJ45 Connectors

Copper cable is popular. It's cheap, easy to install, and flexible for LAN environments. It also supports Power over Ethernet (PoE). This feature lets devices like IP phones, wireless access points, and security cameras receive both data and power through one cable.

Several types of copper cables exist, but for the CCNA exam, you only need to focus on the most common ones. First, let's see the coaxial cable.

Coaxial Cable

In early Ethernet networks, coaxial cable was widely used. It has a central copper conductor. This is surrounded by insulation, shielding, and an outer jacket.

Figure 2 – Coaxial cable

Coaxial offered solid interference protection, but it was bulky and slow. It has now been replaced by twisted-pair cabling in modern LANs.

Unshielded Twisted Pair (UTP)

UTP is the most common type of copper cabling in Ethernet. It contains 4 pairs of wires (8 wires total), with each pair twisted. You may ask yourself: why are the wires twisted?

This is because of a phenomenon called crosstalk, where signals from one pair of wires interfere with another pair. This interference damages the quality of the signal. To solve this issue, the wires are twisted together. This reduces interference and makes the signal more reliable.

Figure 3 – UTP cable

The UTP cable is cheap, flexible, and easy to install, which makes it the default choice for LANs in homes, offices, and classrooms. The drawback is that it lacks shielding. As a result, it can be affected by two types of interference: electromagnetic interference (EMI) and radio frequency interference (RFI).

Shielded Twisted Pair (STP)

STP uses the same twisted-pair design as UTP but adds extra shielding (foil or braided) around the pairs. This shielding reduces crosstalk between the wires and also protects the cable from external interference.

These external interferences can be very disruptive in certain environments.

• Electromagnetic interference (EMI): noise created by electrical devices, such as motors, fluorescent lights, or power cables.
  

• Radio frequency interference (RFI): signals from wireless devices, radio transmitters, or other sources that leak into the cable.

Figure 4 – STP cable

Adding shielding, as shown above, helps STP reduce interference. This keeps data transmission reliable.

The trade-off is that STP is more expensive, less flexible, and harder to install than UTP. It is mainly used in industrial or high-interference environments where protection is critical.

Copper cables are classified into categories (Cat). Each category defines the greatest supported speed and distance.

For the CCNA exam, you mainly need to know Cat5e, Cat6, and Cat6a. These are the most common in today’s networks.

Table 1 – Copper cable categories with Ethernet standards

How Categories and Ethernet Standards Fit Together

Ethernet technology has advanced gradually. With each new generation, improved cabling is needed for higher speeds.

• 1990s – Cat3/Cat5 + 10BASE-T → 10 Mbps

• Late 1990s – Cat5 + 100BASE-TX → 100 Mbps

• 2000s – Cat5e + 1000BASE-T → 1 Gbps

• 2000s – Cat6 + 1000BASE-T → 1 Gbps (better quality)

• 2010s – Cat6 (short) + 10GBASE-T → 10 Gbps up to 55 m

• 2010s – Cat6a + 10GBASE-T → 10 Gbps up to 100 m

In short, the cable categories (Cat) go hand in hand with the Ethernet standards.

For the CCNA exam, you don’t need to memorize everything. However, you should know which cable categories match the main Ethernet standards. This helps you understand how networks grew from 10 Mbps to 10 Gbps.

In order to connect devices together, we need copper connectors.
The most common connector for copper cabling is the RJ45 connector, also known as an 8P8C (8 positions, 8 contacts).

Figure 5 - RJ45 Connector

RJ45 connectors are crimped onto Ethernet cables and are used to connect them to devices such as switches, routers, and PCs.

Each RJ45 plug is inserted into an RJ45 port, which contains 8 pins that match the 8 wires inside the cable.

Figure 6 – RJ45 Port

On your computer, you will typically find this type of port. It is a female RJ45 port, which requires a male RJ45 connector from an Ethernet cable to plug into it.

Figure 7 - UTP Cable plugged into RJ45 port

As a result, when you are in front of a network switch, you can see multiple copper cables connected to the RJ45 ports.

Ethernet cabling must follow a standard so that devices from different vendors can work together. This standard is called TIA/EIA-568, and it defines the order of the 8 wires inside an RJ45 connector.

There are two accepted wiring schemes:

Figure 8 - RJ45 Pinouts for T-568A and T-568B

The difference between them lies only in the color sequence of the wire pairs. Functionally, both standards provide the same performance.

• T-568A has the green pair on pins 1 and 2, and the orange pair on pins 3 and 6.
  

• T-568B swaps these two pairs: the orange pair is on pins 1 and 2, and the green pair is on pins 3 and 6.

You don’t need to memorize every single color code, but it’s important to know that the wiring can be inverted. You will see in the next section why this matters when creating cables.

Based on the pinouts defined earlier, Ethernet cables can be wired in two different ways.

Straight-Through

A straight-through cable uses the same wiring standard (T-568A or T-568B) on both ends.
It is used to connect different types of devices, such as a PC to a switch.

Figure 9 - Straight-Through Cable

Crossover

A crossover cable uses T-568A on one end and T-568B on the other.
It is used to connect similar devices such as one switch to another switch, or one PC to another PC.

Figure 10 - Crossover Cable

Auto-MDIX

Today, most modern devices support Auto-MDIX (Automatic Medium-Dependent Interface Crossover). This feature automatically finds out if the connection should be straight-through or crossover. Then, it adjusts the port behavior as needed.

 As a result, you can usually use a straight-through cable in all cases.

CLI Preview – Verifying a Copper Ethernet Link (Optional)

Let’s look inside the switch to see how it detects and reports an Ethernet link.
In this example, a PC (PC1) is connected to a switch using a straight-through copper cable, as shown in Figure 11.

Figure 11 - Straight-Through Cable

Click on the CLI button below to access the switch and follow the instructions provided.

Observing the CLI output

If the commands are entered correctly, you will see an output similar to the line below:

Fa0/1                        connected    1          auto    auto  10/100BaseTX

• Fa0/1
  The switch port connected to PC1.

• Status = connected
  Confirms that the copper cable is detected and the Ethernet link is up.

• Speed = auto
  Shows that the switch is automatically negotiating the link speed based on the cable and the connected device.

• Duplex = auto
  Shows that the switch is automatically negotiating duplex mode.

• Type = 10/100BaseTX
  Indicates a copper Ethernet interface.

All other ports show notconnect because no device is plugged into them.

Copper cabling is an excellent solution for short-distance and low-cost connections. It is flexible, easy to install, and works perfectly for connecting end devices like PCs, IP phones, or access points to a nearby switch.

But copper has two important limitations you must remember:

• Maximum distance of 100 meters → Beyond this, the signal weakens (attenuation) and communication becomes unreliable.
  

• Sensitive to interference → Copper is vulnerable to electromagnetic interference (EMI) and crosstalk, which can degrade signal quality and reduce performance.

Because of these limits, copper is not the best choice for long-distance links or very high-speed backbones. Fiber optic cabling is preferred in these cases. It offers higher bandwidth and is immune to electrical interference.

In the next lesson, we will look at fiber-optic cabling and see why it has become essential in modern networks.,