How To List DNS Server Order in systemd-resolve

In this article, we will explore how to list the DNS server order in systemd-resolve. This is an essential task for system administrators, as it allows them to understand the order in which DNS queries are resolved, which can be crucial for network troubleshooting and optimization.

What is systemd-resolve?

systemd-resolve is a network name resolution manager that comes with the systemd package. It provides network name resolution to local applications by following the rules and configurations defined in /etc/nsswitch.conf and /etc/systemd/resolved.conf.

Listing DNS Server Order

To list the DNS server order, you can use the systemd-resolve --status command. This command will display the current status of the systemd-resolved manager, including the DNS servers and their order.

Here is the command:

systemd-resolve --status | grep "DNS Servers" -A 2

Let’s break down this command:

• systemd-resolve --status: This command displays the status of the systemd-resolved manager.
• |: This is a pipe operator, which takes the output of the command on its left and uses it as input for the command on its right.
• grep "DNS Servers" -A 2: This command filters the output of the previous command, showing only lines that contain the string “DNS Servers” and the two lines after them (-A 2).

The output of this command will show the DNS servers and their order.

Understanding the DNS Server Order

It’s important to note that systemd-resolve doesn’t strictly follow the order of DNS servers as listed. Instead, it follows internal rules to choose the “correct” DNS server for each query. This decision can be based on factors like past server performance, interface order, and domain allocation.

Viewing the resolv.conf File

If you want to view the resolv.conf file generated by systemd-resolved, you can use the following command:

cat /run/systemd/resolve/resolv.conf

This command will display the contents of the generated resolv.conf file, which can be useful for troubleshooting DNS issues.

Advanced DNS Management with dnsmasq

For more advanced DNS management, you might consider using dnsmasq. This program can be used alongside systemd-resolve and allows you to define rules for resolving specific domains in certain servers. This can be especially useful in complex network setups, such as VPNs.

However, using dnsmasq requires additional installation and configuration. You can find more information about dnsmasq in its official documentation here.

Conclusion

In this article, we have explored how to list the DNS server order in systemd-resolve. We have also discussed how systemd-resolve chooses the DNS server for each query and how to view the resolv.conf file. Finally, we touched on the use of dnsmasq for advanced DNS management.

Understanding these aspects of systemd-resolve can be crucial for system administrators, as it allows them to optimize and troubleshoot their network configurations.