Split DNS

To set up split DNS with Dnsmasq, you need to configure different DNS resolutions for internal and external network users. Split DNS is commonly used to handle different DNS responses based on where the request originates. Here’s a guide on configuring Dnsmasq for split DNS.

Prerequisites

Dnsmasq installed on your server (if not installed, use sudo apt-get install dnsmasq).
Network interfaces configured with internal and external IPs.

Step 1: Configure Dnsmasq

Edit/Create the .conf file Open the Dnsmasq configuration file, usually located at /etc/dnsmasq.conf or Create a new file under /etc/dnsmasq.d/:
```
sudo nano /etc/dnsmasq.conf
```

Note

Creating New file under the `/etc/dnsmasq.d/ is highly recommended

Define DNS server settings for internal and external networks: Use the following configuration options in dnsmasq.conf:
Define internal DNS resolutions: Specify internal domains (or subdomains) that should resolve differently for users on the internal network. For example, suppose your internal domain is internal.example.com, and internal requests should resolve to the local IP 192.168.1.10:
```
# Serve internal.example.com requests with the internal DNS server
server=/internal.example.com/192.168.1.10
```
Configure external DNS resolutions: Define the public DNS server for other domains. For example, using Google DNS for all other requests:
```
# External DNS for all other queries
server=8.8.8.8
```
Bind Dnsmasq to Specific Interfaces: If your server has multiple network interfaces (e.g., eth0 for external and eth1 for internal), you can bind Dnsmasq to listen on the internal interface only:

# Listen on internal interface
interface=eth1

Add Local DNS Entries (Optional): For specific hostnames in the internal domain, you can use the address directive. For example:

# Map a specific hostname to an IP
address=/server1.internal.example.com/192.168.1.20

Step 2: Restart Dnsmasq

After editing the configuration, restart the Dnsmasq service to apply changes:

sudo systemctl restart dnsmasq

Step 3: Testing the Configuration

From an internal device: Run the following to verify the internal DNS resolution:
```
nslookup server1.internal.example.com
```
From an external device: Verify the DNS resolves to the public IP:
```
nslookup example.com
```

This setup will direct internal DNS requests for internal.example.com to the internal DNS server while other requests go to the external DNS (Google DNS in this example). Let me know if you need further customization!