4 Basic Ethernet Cable Troubleshooting and Easy Fixes

Ethernet cable troubleshooting is essential for maintaining a stable network connection. When facing problems, such as the low speed or Ethernet cable not working, identifying the root causes is crucial. This process involves systematic troubleshooting to uncover issues and implement effective solutions.

Common problems include physical damage, loose connections, or faulty equipment. By understanding these problems and solutions, users can quickly restore their network connectivity and ensure smooth operation.

In this article, we will discuss 4 basic ethernet troubleshooting fixes to help you get maximum speed on ethernet cable and the best network connectivity. These fixes are important to know for every network engineer to maintain smooth connectivity.

These networking technologies and troubleshooting are also taught in our IT infrastructure courses. The students can learn the functioning of various devices and their troubleshooting practices.

Common Ethernet Problems and Solutions

The 4 most common issues with ethernet cable are:

1. Collisions

2. Errors (not working, less speed, etc)

3. Mismatched Duplex

4. Speed Mismatches

Let's understand each of these ethernet cable problems and check their troubleshooting steps:

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1. Collisions

Collisions refer to the data transmitted from multiple devices at the same time on a shared medium such as ethernet for example if multiple desktops are connected to a hub, when two desktops send data at the same time then that data collision occurs resulting the data loss and resending of the same will happen.

Excessive collisions can lead to degraded network performance and slow data transmission. Here the below picture demonstrates that PC1 and PC2 are connected to a Hub and when these two devices transmit data, collision will occur this is called collision domain.

If this hub is replaced by a switch, then the collision domain is restricted only to switch ports.

Troubleshooting Steps:

✓ Check the interface statistics for collision counts. This can be done using the "show interface" command on Cisco devices such as switches.

✓ Identify the interfaces with a high number of collisions.

✓ Determine the cause of collisions, which could be due to network congestion, improper cabling, or faulty network interface cards (NICs).

✓ Troubleshoot the issue by addressing the underlying cause, such as optimizing network traffic, replacing faulty cables, or updating NIC drivers.

2. Errors

Errors on network interfaces can indicate issues with data transmission, such as packet loss, corrupt packets, or transmission failures. High error rates can result in data loss, network instability, and decreased performance.

Troubleshooting Steps:

✓ Use the "show interface" command to check the error counters on the interface, such as input errors and output errors.

✓ Identify the interfaces with a significant number of errors.

✓ Investigate the cause of errors, which could be due to issues like electrical interference, faulty cables, or misconfigured network settings.

✓ Troubleshoot by replacing damaged cables, checking for loose connections, or adjusting network configurations as needed.

3. Mismatched Duplex

Duplex refers to the method by which data is transmitted and received on a network interface. The duplex setting is mismatched between the two connected devices when one device has full-duplex and the other has half duplex.

By default interfaces are configured as "duplex auto" which prefers full duplex if one end is configured as auto and the other end is configured as half then it is negotiated as half duplex.

This can lead to performance issues and intermittent connectivity problems. This can be checked using the command "show interface ".

In the below example routers R1 and R2 are directly connected on interfaces Gi0/0, R1 Gi0/0 is manually configured as full duplex and R2 Gi0/0 is manually configured as half duplex. R2/R1 throws a CDP error about duplex mismatched as shown below on R2.

It is recommended to configure it as duplex auto (which is the default) on the device's interface unless it is necessary. 

Troubleshooting Steps:

✓ Check the duplex settings of the interfaces using the "show interface" command.

✓ Identify interfaces with mismatched duplex settings.

✓ Configure both connected devices to use the same duplex setting (either full duplex or half duplex) to ensure compatibility and optimal performance.

4. Speed Mismatches

A speed mismatch occurs when two connected devices operate at different data transmission speeds. As an example, when at one end speed is configured as 100 Mbps while other is configured as 1 Gbps. Though by default on interfaces, speed is set to be auto and negotiated at minimum between to-end devices. 

If speed is mismatched, then interface links do not come up hence data does not transmit between two ends. You can check the interface speed as shown below.

Troubleshooting Steps:

✓ Verify the speed settings of the interfaces using the "show interface" command.

✓ Identify interfaces with mismatched speed settings.

✓ You have to make sure that the speed configured on both device's interfaces should be same either 100 Mbps or 1 Gbps based on the maximum speed supported on these device interfaces. 

Ethernet Cable Troubleshooting Process

Suppose you encounter network connectivity issues between a switch and a server. The server is experiencing intermittent connectivity and slow data transfer. To troubleshoot, follow these steps:

1. Check the interface statistics on the switch and server using the "show interface" command.

2. Identify any collision, error, duplex, or speed mismatch counters that are significantly high on either interface.

3. Address collisions by analyzing network congestion, ensuring proper cabling, and resolving any faulty NICs.

4. Investigate errors and rectify issues like electrical interference, faulty cables, or misconfigurations.

5. Resolve duplex mismatches by configuring both the switch and server interfaces with the same duplex setting (either full or half duplex).

6. Ensure both devices operate at the same data transmission speed by configuring their interfaces accordingly.

7. Test the connectivity and data transfer between the switch and server to verify if the issues have been resolved.

By following these troubleshooting steps and addressing interface and cable issues, you can diagnose and resolve common problems related to collisions, errors, duplex mismatches, and speed mismatches in a CCNA context.

To try these troubleshooting visit our CCNA Virtual Lab

Ethernet Cable Troubleshooting - Summing Up

As a network engineer, you should be able to troubleshoot network cables like ethernet. Ethernet cables are a very important networking device that connects most of the computers to a network. As per the CCNA standards, there are 4 common issues with ethernet cables - collisions, errors, speed mismatch, and mismatched duplex.

In this article, we have covered all these major ethernet LAN issues and detailed steps to fix these issues. With proper diagnosing, you can figure out what is causing the problems in your network and troubleshoot them.