New Install Ubuntu 24.04 Netplan Set Correctly, Gettting "Temporary Failure In Name Resolution" From DNS

When setting up a new Ubuntu 24.04 virtual machine (VM), encountering the "Temporary failure in name resolution" error can be a frustrating experience, especially after meticulously configuring the network settings using Netplan. This error typically indicates a problem with the Domain Name System (DNS) resolution, preventing your system from translating domain names (like google.com) into IP addresses. This article will delve into the common causes of this issue and provide a comprehensive guide to troubleshooting and resolving it, ensuring your Ubuntu 24.04 VM can access the internet and other network resources seamlessly. We'll explore various aspects, including the correct Netplan configuration, common pitfalls in DNS settings, and effective methods for diagnosing and fixing the problem. By the end of this guide, you'll have a solid understanding of how to tackle DNS resolution issues in Ubuntu 24.04 and maintain a stable network connection.

Understanding the "Temporary Failure in Name Resolution" Error

Before diving into the solutions, it's crucial to understand what the "Temporary failure in name resolution" error signifies. This error essentially means your system is unable to contact the configured DNS servers to resolve domain names. This can manifest in various ways, such as being unable to browse websites, ping external addresses by name, or use any network services that rely on DNS resolution. The root cause often lies in misconfigured network settings, inaccessible DNS servers, or issues with the system's DNS resolver. To effectively troubleshoot this, we need to systematically examine each potential cause, starting with the Netplan configuration, which is the primary tool for network management in Ubuntu 24.04. We will cover checking the syntax, ensuring the correct interface is configured, and verifying that the DNS server addresses are reachable. Additionally, we'll explore alternative DNS servers and how to configure them, as well as look into the role of systemd-resolved, the default DNS resolver in Ubuntu, and how to troubleshoot its settings. Furthermore, this guide will address common mistakes in Netplan configuration and provide practical steps for applying changes correctly to avoid further complications. By the end of this section, you should have a clear understanding of the error and the key areas to investigate in your quest for a solution.

Netplan Configuration: The Foundation of Network Settings

In Ubuntu 24.04, Netplan is the cornerstone of network configuration. It uses YAML files to define network interfaces and their settings. A misconfigured Netplan file is a primary suspect when encountering DNS resolution issues. Let's examine a typical Netplan configuration and highlight the critical aspects for DNS resolution.

A basic Netplan configuration file, usually located in /etc/netplan/, might look like this:

network:
 version: 2
 renderer: networkd
 ethernets:
 ens192:
 dhcp4: false
 addresses:
 - 192.168.1.100/24
 gateway4: 192.168.1.1
 nameservers:
 addresses:
 - 8.8.8.8
 - 8.8.4.4

Here, ens192 is the name of the network interface. dhcp4: false indicates a static IP configuration. addresses specifies the IP address and subnet mask. gateway4 defines the default gateway. Most importantly, the nameservers section is where you configure the DNS servers. The addresses under nameservers lists the IP addresses of the DNS servers to be used. In this example, we are using Google's Public DNS servers (8.8.8.8 and 8.8.4.4). It's crucial to ensure that these addresses are correct and reachable from your VM. To further refine your Netplan configuration, you might consider adding search domains, which allow you to use shorter names when resolving hosts within your local network. Additionally, understanding the order of operations in Netplan, particularly how it interacts with systemd-resolved, is essential for advanced troubleshooting. Common pitfalls include syntax errors in the YAML file, incorrect interface names, and conflicting network configurations. We'll explore these in detail to help you avoid common mistakes and maintain a robust network setup.

Common Netplan Configuration Errors and How to Fix Them

Several common errors can creep into your Netplan configuration, leading to DNS resolution problems. Identifying and rectifying these errors is a crucial step in restoring network functionality. One of the most frequent issues is syntax errors in the YAML file. YAML is indentation-sensitive, so even a single misplaced space can invalidate the configuration. Always double-check the indentation and spacing in your Netplan file. Tools like online YAML validators can be invaluable for catching these errors. Another common mistake is using the wrong interface name. The interface name (e.g., ens192) must match the actual name of your network interface. You can use the ip addr command to list all available network interfaces and their names. Using an incorrect interface name will result in the configuration being applied to the wrong interface or no interface at all. Furthermore, incorrect IP addresses, gateway, or DNS server addresses are frequent culprits. A typo in any of these addresses can prevent your system from communicating with the network or resolving domain names. Double-check these values against your network settings and ensure they are correct. Finally, conflicting network configurations can also cause issues. If you have multiple Netplan files or other network management tools interfering with Netplan, it can lead to unpredictable behavior. Ensure that you only have one active Netplan configuration file and that no other tools are overriding its settings. By being meticulous in your configuration and understanding these common pitfalls, you can significantly reduce the likelihood of encountering DNS resolution problems.

Applying Netplan Configuration Changes

After making changes to your Netplan configuration, it's essential to apply these changes correctly. Simply editing the YAML file is not enough; you need to instruct Netplan to reconfigure the network interfaces using the new settings. Netplan provides two primary commands for this purpose: sudo netplan apply and sudo netplan try. sudo netplan apply applies the configuration immediately. If there are errors in the configuration, it may disrupt your network connection. Therefore, it's generally recommended to use sudo netplan try first. sudo netplan try applies the configuration but includes a rollback mechanism. It will revert to the previous configuration if it doesn't receive confirmation within a certain timeframe (usually 120 seconds). This prevents you from being locked out of your system if there are errors in the new configuration. When you run sudo netplan try, it will prompt you to confirm that the configuration is working. If you can still access the network and resolve domain names, you should confirm. If you lose network connectivity, do nothing, and the system will automatically revert to the previous configuration. After successfully applying the configuration with sudo netplan try, you can then use sudo netplan apply to make the changes permanent. It's crucial to understand the difference between these commands and use them appropriately to avoid disrupting your network connection. Always test your changes before making them permanent, and be prepared to revert if necessary. Additionally, checking the system logs (e.g., using journalctl -u systemd-networkd) can provide valuable insights into any errors or issues that occurred during the Netplan application process.

Verifying DNS Server Reachability

Even with a correctly configured Netplan file, your system might still fail to resolve domain names if the configured DNS servers are unreachable. It's crucial to verify that your system can communicate with the DNS servers you've specified in your Netplan configuration. A simple way to test this is to use the ping command. For example, if you've configured Google's Public DNS servers (8.8.8.8 and 8.8.4.4), you can ping them using the following commands:

ping 8.8.8.8
ping 8.8.4.4

If the pings are successful, you'll see responses indicating that your system can reach these servers. If the pings fail (you see