Check Network Interface Speed in Linux 2026: 7 Fast Commands

Updated March 2026 with faster NIC speed checks for ethtool, ip, and nmcli.

Network speed plays a critical role in system performance. Knowing the speed of your network interfaces can help you troubleshoot and optimize your environment. In this guide, we'll show you how to check the speed of your network interface using Linux tools.

Quick Answer

Use these commands first when you need the negotiated NIC speed fast:

# Fastest check for Ethernet links
sudo ethtool eth0 | grep -E 'Speed|Duplex|Auto-negotiation'

# Show link state and MTU
ip -br link show eth0

# NetworkManager systems
nmcli device show eth0 | grep -E 'GENERAL.DEVICE|WIRED-PROPERTIES.SPEED'

If ethtool reports Unknown or the speed looks wrong, verify the cable, switch port, VM vNIC type, autonegotiation, and duplex settings before chasing packet loss elsewhere.

Why Check Network Interface Speed?

Network interface speed impacts how much data your system can send and receive. Here are key reasons to check it:

• Diagnosing slow network issues.
• Verifying hardware capabilities.
• Optimizing performance for high-demand applications.

Tools to Check Network Interface Speed

Linux offers several tools to check network speed. We'll explore the most commonly used ones:

1. Using ethtool

ethtool is a popular utility for managing and troubleshooting Ethernet devices. You can use it to check the current speed of your network interface.

Install ethtool

On most distributions, install it using your package manager:

sudo apt install ethtool    # For Debian/Ubuntu  
sudo yum install ethtool    # For CentOS/RHEL  

Check Interface Speed

Run the following command, replacing eth0 with your network interface name:

sudo ethtool eth0  

Look for the line that says Speed. For example:

Speed: 1000Mb/s  

This indicates the interface is running at 1 Gbps.

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2. Using ifconfig

ifconfig is an older tool but still useful. While it doesn't directly show speed, it provides details about interfaces.

Install net-tools

If ifconfig isn't available, install the net-tools package:

sudo apt install net-tools    # For Debian/Ubuntu  
sudo yum install net-tools    # For CentOS/RHEL  

Use ifconfig

Run the command:

ifconfig eth0  

For speed details, combine it with ethtool or check the RX and TX statistics for performance trends.

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3. Using ip

The ip command is modern and replaces ifconfig. While it doesn’t directly show speed, it provides insights into link states.

ip link show eth0  

For detailed speed information, pair it with ethtool.

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4. Checking in /sys/class

The /sys/class directory contains hardware details. Use it to manually check the speed of an interface:

cat /sys/class/net/eth0/speed  

If the output shows 1000, your interface supports 1 Gbps.

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5. Testing with iperf

If you want to measure actual network throughput, use iperf. Install it as follows:

sudo apt install iperf3    # For Debian/Ubuntu  
sudo yum install iperf3    # For CentOS/RHEL  

Set up a server:

iperf3 -s  

On another machine, run:

iperf3 -c <server_ip>  

This tests the actual data transfer speed.

Related Linux Network Guides

• A Guide to Adjusting NIC Buffer Sizes on Linux - Tune RX and TX ring buffers when drops appear
• ethtool Coalesce Settings Guide - Reduce interrupt overhead on busy hosts
• Netdev Budget Tuning - Improve packet processing under high load

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Common Issues with Network Speed

Sometimes, the reported speed is lower than expected. Common causes include:

• Cable Limitations: Ensure you use high-quality Ethernet cables.
• Switch Compatibility: Check if your switch supports your interface speed.
• Driver Problems: Outdated drivers may restrict performance.

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Conclusion

Checking network interface speed in Linux is easy with tools like ethtool, ifconfig, and ip. Regular monitoring ensures optimal performance and helps diagnose issues quickly.

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Related Linux Network Performance Guides

• Adjust NIC Buffer Sizes on Linux - Tune ring buffers when drops appear under load
• ethtool Coalesce Settings Explained - Reduce interrupt overhead without adding too much latency
• Netdev Budget Tuning on Linux - Fix packet processing bottlenecks on busy hosts
• Configure Bond Interfaces on Ubuntu - Verify speed and failover behavior on bonded links