Troubleshooting Slow Network Connectivity with ss and resolvectl on Linux -

Introduction to Network Troubleshooting

I’ve seen my fair share of slow network connectivity issues on Linux, and having the right tools at your disposal can make all the difference. Two tools that I rely on are ss and resolvectl, which can help you diagnose and troubleshoot network issues. In this article, we’ll explore how to use these tools to identify and potentially fix slow network connectivity problems.

Understanding `ss`

The ss command is a replacement for the traditional netstat command, and it provides more detailed information about network connections, including TCP, UDP, and Unix domain sockets. To get started with ss, you can use the following command to display all active connections:

ss -tulpn

This command will show you a list of all active TCP connections, including the protocol, local address, peer address, and process ID. Don’t bother with the netstat command unless you’re working with an older system that doesn’t have ss available.

Using `resolvectl`

resolvectl is a command-line utility that allows you to query and control the systemd-resolved service, which is responsible for DNS resolution on many modern Linux distributions. You can use resolvectl to check the current DNS settings and query the DNS cache:

resolvectl status
resolvectl query example.com

The first command will show you the current DNS settings, including the DNS servers and search domains. The second command will query the DNS cache for the IP address of example.com. I usually start with these commands to get a sense of what’s going on with my DNS settings.

Troubleshooting Slow Network Connectivity

To troubleshoot slow network connectivity, you can use ss and resolvectl together to identify potential bottlenecks. Here’s an example workflow:

Use ss to identify any active connections that may be causing the slow network connectivity:

ss -tulpn | grep <port_number>

Replace <port_number> with the port number of the service that’s experiencing slow connectivity. This is where people usually get burned - they forget to check the actual connections and end up chasing their tails.

Use resolvectl to check the DNS settings and query the DNS cache:

resolvectl status
resolvectl query <domain_name>

Replace <domain_name> with the domain name of the service that’s experiencing slow connectivity.

Check the network interface configuration using the ip command:

ip link show
ip addr show

These commands will show you the current network interface configuration, including the IP address, netmask, and gateway. In practice, this is usually where I find the issue - a misconfigured interface or a missing route.

Use the ping command to test the network connectivity:

ping -c 4 <domain_name>

Replace <domain_name> with the domain name of the service that’s experiencing slow connectivity. The real trick is to use ping in combination with ss and resolvectl to get a complete picture of what’s going on.

Security Considerations

When troubleshooting network connectivity issues, it’s essential to keep security in mind. Make sure to only use trusted DNS servers and avoid using public DNS servers that may be vulnerable to DNS spoofing attacks. You can use the systemd-resolved documentation to learn more about configuring DNS settings securely.

Additional Tools and Resources

For more advanced network troubleshooting, you can use tools like tcpdump and Wireshark. These tools allow you to capture and analyze network traffic, which can help you identify potential issues with your network configuration. You can also refer to the Linux kernel documentation for more information on network configuration and troubleshooting.

Practical Examples and Trade-Offs

When using ss and resolvectl, it’s essential to consider the trade-offs between different commands and options. For example, using the -t option with ss will show you only TCP connections, while using the -u option will show you only UDP connections. Similarly, using the query command with resolvectl will query the DNS cache, while using the status command will show you the current DNS settings. Don’t get too caught up in the options - focus on getting the job done.

By understanding these trade-offs and using the right tools for the job, you can effectively troubleshoot slow network connectivity issues on Linux and improve your overall network performance.