Name Server Guide

DNS Configuration Guide for Debian-Based Linux Systems

This guide provides step-by-step instructions for configuring custom DNS servers on Debian-based Linux distributions (Debian, Ubuntu, Linux Mint, etc.). The example uses Cloudflare DNS (1.1.1.1 and 1.0.0.1), but you can substitute with your preferred DNS servers.

Prerequisites

• Debian-based Linux distribution
• Root or sudo privileges
• Basic understanding of network configuration

System Compatibility

This guide has been tested on:

• Debian 10 (Buster) and newer
• Ubuntu 20.04 LTS and newer

Configuration Steps

1. Check Network Interface Configuration

First, examine the primary network interface configuration:

sudo nano /etc/network/interfaces

2. Check Secondary Configuration (if needed)

If no DNS configuration exists in the primary file, check the interfaces directory:

sudo nano /etc/network/interfaces.d/50-cloud-init

Note: The 50-cloud-init configuration is common in cloud-hosted Debian instances.

3. Remove Existing DNS Configuration

In either file, locate and remove or comment out any existing DNS configuration:

# Comment out or remove lines like:
# dns-nameservers xxx.xxx.xxx.xxx

Save the changes:

• In nano: Press Ctrl + X, then Y, then Enter

4. Configure DHCP Client

Edit the DHCP client configuration:

sudo nano /etc/dhcp/dhclient.conf

Add the following line (using Cloudflare DNS as example):

supersede domain-name-servers 1.1.1.1, 1.0.0.1;

Save the changes:

• In nano: Press Ctrl + X, then Y, then Enter

5. Restart Networking Service

Apply the changes by restarting the networking service:

sudo systemctl restart networking

Note: On some newer Debian-based systems, you might need to use:

sudo systemctl restart NetworkManager

6. Verify Configuration

Check the current DNS configuration:

cat /etc/resolv.conf

Test DNS resolution:

sudo nslookup google.com

Expected output should show responses from your configured DNS servers.

Notes

Common Issues

1. Network Disconnection: If you lose network connectivity after restart:

   sudo systemctl restart networking
   # or
   sudo systemctl restart NetworkManager
   

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2. DNS Not Updating: Verify dhclient is using the new configuration:

   sudo systemctl restart network-manager
   

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3. Resolution Failures: Test with multiple domains:

   nslookup cloudflare.com
   nslookup github.com
   

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Security Notes

On Debian systems, consider:

1. Setting proper file permissions
2. Using DNS over HTTPS (DoH) if supported
3. Configuring UFW firewall for DNS ports

Additional Resources

• Debian Wiki Network Configuration
• Cloudflare DNS Documentation: https://1.1.1.1/dns/
• Ubuntu Network Configuration Guide