Networking

Introduction to nftables and ifupdown

As a Linux admin, you’re probably no stranger to managing network traffic and configuring firewall rules. Two tools that can make your life easier are nftables and ifupdown. nftables is a packet filtering framework that’s meant to replace traditional iptables, while ifupdown is a Debian-specific tool for managing network interfaces. I’ve seen this go wrong when people don’t take the time to understand how these tools work together. In this article, we’ll dive into troubleshooting common issues with nftables rules and Debian’s ifupdown, focusing on practical solutions and real-world examples.

Introduction to DNS Quirks and systemd-resolved

I’ve seen my fair share of DNS issues over the years, and in complex network environments, they can become a real headache. These problems often stem from misconfigured DNS servers, conflicting resolver settings, or the challenges of managing split DNS configurations. With systemd-resolved, managing DNS resolution has become more robust and secure. I’ve found it to be an essential tool in my Linux toolkit.

Introduction to resolvectl

I’ve seen DNS leaks compromise network privacy time and again, so I’m always on the lookout for ways to tighten up my DNS configuration. As a Linux user, you’re likely familiar with the importance of DNS resolution for accessing websites and services. resolvectl is a powerful tool that comes with systemd, and it’s been a game-changer for managing DNS resolution on my systems.

What is resolvectl?

resolvectl is a command-line utility that allows you to control and configure DNS resolution on your system. It’s part of the systemd suite, which is widely used on modern Linux distributions. With resolvectl, you can set DNS servers, query DNS records, and troubleshoot DNS issues - all from the comfort of your terminal.

Introduction to systemd-resolved

I’ve seen this go wrong when working with multi-homed Linux machines: DNS lookup surprises can be a real pain. A multi-homed machine, with multiple network interfaces each connected to a different network, can lead to DNS resolution problems. The system may not know which interface to use for DNS lookups, causing all sorts of issues. This is where people usually get burned - trying to troubleshoot DNS problems without a clear understanding of how their system is configured. To address this issue, I usually start with systemd-resolved, a tool that can help manage DNS resolution and provide more predictable behavior.

Introduction to DNS Leaks

I’ve seen DNS leaks become a major concern for Linux users, especially those relying on systemd-resolved. A DNS leak occurs when your system sends DNS queries to an unintended DNS server, potentially exposing your browsing history and other sensitive information. In this article, I’ll share my experience and insights on how to identify and troubleshoot DNS leaks using systemd-resolved and resolv.conf.

Understanding systemd-resolved

Systemd-resolved is a powerful tool that provides DNS resolution. It acts as a local DNS resolver, caching DNS queries and responses to improve performance. By default, systemd-resolved uses the DNS servers provided by your network configuration, but you can configure it to use specific DNS servers. To check the current DNS servers used by systemd-resolved, run:

Introduction to SSH Tunneling

I’ve seen this go wrong when people try to access remote networks without using a secure method - that’s where SSH tunneling comes in. This technique leverages an intermediate host, known as a jump host, to securely access remote networks. It’s particularly useful when direct access is restricted due to firewall rules or network policies. By using SSH to tunnel traffic through a jump host, you can establish a secure connection to a remote server or network, even if direct access is not possible.

Introduction to DNS Troubleshooting

We’ve all been there - trying to access a website or service, only to be met with an “Unknown Host” error. These errors often stem from DNS issues, which can be frustrating to troubleshoot, especially when you’re not sure where to start. In my experience, the culprits are usually misconfigured resolv.conf files or problems with systemd-resolved. In this article, I’ll walk you through the practical aspects of troubleshooting DNS issues, focusing on systemd-resolved and resolv.conf, to help you resolve the “Unknown Host” headache efficiently.

Introduction to systemd-resolved

I’ve been using systemd-resolved for a while now, and I have to say, it’s a game-changer when it comes to managing DNS resolution on Linux systems. As of 2026, it’s become a crucial component in many Linux distributions, including Ubuntu, Debian, and Fedora. In this article, I’ll walk you through how to use systemd-resolved with multiple DNS servers and split horizon DNS, including some practical examples and troubleshooting notes.

Introduction to Troubleshooting Local Port Conflicts

When dealing with a Linux server that’s running multiple services, I’ve seen this go wrong when two or more services try to bind to the same port - it’s a recipe for disaster. This is where people usually get burned, as one or more of the services will fail to start. To avoid this, we can use the ss command and nftables to troubleshoot local port conflicts.

Introduction to DNS Leaks

I’ve seen DNS leaks become a major concern for Linux users who care about their online privacy. Essentially, a DNS leak happens when your system’s DNS queries slip outside a secure tunnel - think VPN - and potentially expose your browsing history to prying eyes. Given the current online security landscape, being able to troubleshoot these leaks is more important than ever.

Understanding systemd-resolved

Systemd-resolved is a key system service in Linux that handles DNS resolution. It’s part of the systemd suite and is widely used in modern distributions like Ubuntu, Debian, and Fedora. One of the benefits of systemd-resolved is that it can be configured to use DNS over TLS (DoT) or DNS over HTTPS (DoH), which encrypts DNS queries and reduces the risk of leaks.