How to Solve the Downshift Error in Ethernet Speed on Linux

Learn how to solve the downshift error that occurs when your Ethernet speed drops from 1Gbps to 100Mbps on Linux and how to prevent it from happening again.

Ethernet is a common technology that allows you to connect your devices to a network using a cable. Ethernet can support different speeds, such as 10Mbps, 100Mbps, or 1Gbps, depending on the hardware and the cable quality. However, sometimes you may encounter an error that causes your Ethernet speed to downshift from 1Gbps to 100Mbps, even if your hardware and cable are capable of 1Gbps. This error can affect your network performance and stability, and it can be frustrating to deal with.

In this article, we will show you how to solve the downshift error in Ethernet speed on Linux and how to prevent it from happening again. We will also answer some frequently asked questions about Ethernet speed and troubleshooting.

What Causes the Downshift Error in Ethernet Speed on Linux?

The downshift error in Ethernet speed on Linux is caused by a mismatch between the negotiated speed and the actual speed of the Ethernet connection. The negotiated speed is the speed that the devices agree to use when they establish the connection. The actual speed is the speed that the devices can achieve based on the hardware and the cable quality.

The negotiated speed and the actual speed should be the same, but sometimes they can differ due to various factors, such as:

• A faulty or incompatible network card or driver.
• A faulty or low-quality cable or connector.
• A faulty or misconfigured switch or router.
• A noisy or congested network environment.
• A power surge or outage.

When the negotiated speed and the actual speed differ, the devices may try to adjust the speed to match the actual speed. This process is called downshifting or downgrading, and it can result in a lower speed than expected. For example, if the devices negotiate a speed of 1Gbps, but the actual speed is only 100Mbps, the devices may downshift the speed to 100Mbps to avoid errors and disconnections.

The downshift error can be detected by the network card or the driver, and it can be reported in the system logs. For example, on Linux, you may see a message like this in the dmesg output:

Generic FE-GE Realtek PHY r8169-0-2e00:00: Downshift occurred from negotiated speed 1Gbps to actual speed 100Mbps, check cabling!

This message indicates that the network card (r8169) detected a downshift from 1Gbps to 100Mbps, and it suggests checking the cabling as a possible cause.

How to Solve the Downshift Error in Ethernet Speed on Linux?

To solve the downshift error in Ethernet speed on Linux, you need to identify and fix the cause of the mismatch between the negotiated speed and the actual speed. There are several steps that you can take to troubleshoot and resolve the issue, such as:

Solution 1: Check the network card and the driver

Make sure that your network card and the driver are compatible and up to date. You can use the lspci and ethtool commands to check the network card model and the driver version. You can also use the modinfo and modprobe commands to check and load the driver module. If you have a Realtek network card, you may need to install the r8168-dkms package to replace the default r8169 driver, as some users have reported issues with the r8169 driver.

Solution 2: Check the cable and the connector

Make sure that your cable and the connector are in good condition and support the desired speed. You can use a cable tester or a multimeter to check the cable for continuity and resistance. You can also try a different cable or a different port on the switch or the router. You should use a Cat 5e or higher cable for 1Gbps speed, and avoid using long or coiled cables.

Solution 3: Check the switch or the router

Make sure that your switch or the router is configured correctly and supports the desired speed. You can use the web interface or the command line interface to check the settings and the status of the switch or the router. You can also try a different switch or a router, or connect your devices directly without a switch or a router.

Solution 4: Check the network environment

Make sure that your network environment is free of noise and congestion that can interfere with the signal quality and the speed. You can use the ping and traceroute commands to check the latency and the packet loss of the network. You can also use the iperf or the speedtest commands to check the bandwidth and the throughput of the network. You should avoid placing your cable near sources of electromagnetic interference, such as power cords, transformers, or fluorescent lights.

How to Prevent the Downshift Error in Ethernet Speed on Linux?

To prevent the downshift error in Ethernet speed on Linux, you need to ensure that your network devices and components are compatible and reliable, and that your network environment is optimal. You can follow these tips to avoid the downshift error in the future:

• Use high-quality and certified network devices and components. Choose network devices and components that are compatible with your system and support the desired speed. Look for the certification labels and the specifications of the devices and components, and avoid using cheap or counterfeit products.
• Use the appropriate cable and connector for the speed. Use a Cat 5e or higher cable and a RJ45 connector for 1Gbps speed, and make sure that the cable and the connector are in good condition and properly connected. Avoid using long or coiled cables, or cables that are damaged or kinked.
• Use a suitable switch or router for the speed. Use a switch or a router that supports the desired speed and has enough ports and bandwidth for your network. Configure the switch or the router correctly and update the firmware regularly. Avoid using old or faulty switches or routers, or switches or routers that are overloaded or misconfigured.
• Optimize your network environment for the speed. Optimize your network environment to reduce the noise and the congestion that can affect the signal quality and the speed. Place your cable away from sources of electromagnetic interference, such as power cords, transformers, or fluorescent lights. Use a dedicated network for your devices, and avoid sharing the network with other devices or applications that consume a lot of bandwidth or generate a lot of traffic.

Frequently Asked Questions (FAQs)

Question: How to check the Ethernet speed on Linux?

Answer: To check the Ethernet speed on Linux, you can use the ethtool command. For example, to check the speed of the interface enp46s0, you can run the following command:

ethtool enp46s0

You should see the output like this:

Settings for enp46s0:
Supported ports: [ TP ]
Supported link modes:   10baseT/Half 10baseT/Full 
                        100baseT/Half 100baseT/Full 
                        1000baseT/Full 
Supported pause frame use: No
Supports auto-negotiation: Yes
Supported FEC modes: Not reported
Advertised link modes:  10baseT/Half 10baseT/Full 
                        100baseT/Half 100baseT/Full 
                        1000baseT/Full 
Advertised pause frame use: Symmetric Receive-only
Advertised auto-negotiation: Yes
Advertised FEC modes: Not reported
Link partner advertised link modes:  10baseT/Half 10baseT/Full 
                                     100baseT/Half 100baseT/Full 
                                     1000baseT/Full 
Link partner advertised pause frame use: Symmetric Receive-only
Link partner advertised auto-negotiation: Yes
Link partner advertised FEC modes: Not reported
Speed: 1000Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 0
Transceiver: internal
Auto-negotiation: on
MDI-X: Unknown
Supports Wake-on: pumbg
Wake-on: g
Current message level: 0x00000033 (51)
                       drv probe ifdown ifup
Link detected: yes

The Speed field shows the current speed of the interface, in this case, 1000Mb/s or 1Gbps.

Question: How to change the Ethernet speed on Linux?

Answer: To change the Ethernet speed on Linux, you can use the ethtool command with the -s option. For example, to change the speed of the interface enp46s0 to 100Mbps, you can run the following command:

sudo ethtool -s enp46s0 speed 100 duplex full autoneg off

This command will set the speed of the interface to 100Mbps, the duplex mode to full, and the auto-negotiation to off. You can use different values for the speed, duplex, and autoneg parameters, depending on the supported modes of your interface and your network devices.

However, changing the Ethernet speed manually is not recommended, as it may cause compatibility issues or errors. It is better to use the auto-negotiation mode, which allows the devices to negotiate the best speed and duplex mode automatically.

Summary

In this article, we have explained how to solve the downshift error in Ethernet speed on Linux and how to prevent it from happening again. We have also answered some frequently asked questions about Ethernet speed and troubleshooting. We hope that this article has helped you to solve your problem and improve your network performance and stability.

Disclaimer: This article is for informational purposes only and does not constitute professional advice. We are not responsible for any damage or loss that may result from following the instructions