Public DNS Detector

Public DNS Detector is a lightweight utility designed to identify the DNS servers used by clients visiting a website. It helps distinguish between major DNS providers (such as Cloudflare and Google) and other autonomous servers that directly emit resolution requests.

How It Works

1. DNS Query: When a client's browser requests the object JSON from the URL https://uuid.dnsdetector.zone.tld/dnsdetector, the script initiates a DNS query for the subdomain uuid.dnsdetector.zone.tld.

2. Server Response:

   • On port 53 (DNS), the program responds to A or AAAA queries for uuid.dnsdetector.zone.tld with the IPv4 or IPv6 address of the Public DNS Detector server. The Time-to-Live (TTL) for this response is set to 60 seconds.
   • Simultaneously, the program records the IP address of the DNS client that made the request.

3. JSON Object Retrieval:

   • With the resolved IP address for uuid.dnsdetector.zone.tld, the client's browser can retrieve the JSON object from https://uuid.dnsdetector.zone.tld/dnsdetector.
   • The JSON object contains information about the DNS server used by the client, represented as: {"server": "client DNS IP address"}.

Features

• Detects major DNS providers (e.g., Cloudflare, Google) vs. autonomous servers.
• Lightweight and efficient.
• Easy integration into web applications.

Usage

1. Deploy the Public DNS Detector server (listening on ports 53 and 80 behind an HTTPS proxy).
2. Configure the DNS record for dnsdetector.zone.tld to point to your server's IP address.
3. Implement the client-side script to query uuid.dnsdetector.zone.tld and retrieve the JSON object.

Configuration

You can configure the Public DNS Detector server using command line arguments or environment variables. If both are provided, the environment variables will take precedence.

Here are the options you can set:

• serverAddr: The default address for the DNS server. Set with -serverAddr or the SERVER_ADDR environment variable.
• serverAddrIPv6: The default IPv6 address for the DNS server. Set with -serverAddrIPv6 or the SERVER_ADDR_IPV6 environment variable.
• ttl: The default TTL for the DNS records. Set with -ttl or the TTL environment variable.
• httpAddr: The default address for the HTTP server. Set with -httpAddr or the HTTP_ADDR environment variable.
• httpPort: The default port for the HTTP server. Set with -httpPort or the HTTP_PORT environment variable.
• dnsAddr: The default address for the DNS server. Set with -dnsAddr or the DNS_ADDR environment variable.
• dnsPort: The default port for the DNS server. Set with -dnsPort or the DNS_PORT environment variable.
• zone: The default zone for the DNS server. Set with -zone or the ZONE environment variable.
• templateLocation: The default location for the templates. Set with -templateLocation or the TEMPLATE_LOCATION environment variable.
• maxRequestsPerSecond: The maximum number of requests per second. Set with -maxRequestsPerSecond or the MAX_REQUESTS_PER_SECOND environment variable.
• burstSize: The maximum number of requests in a burst. Set with -burstSize or the BURST_SIZE environment variable. You can display the help message with the -help command line argument.

For example, to start the server with a custom HTTP port and TTL, you could use:

./public-dnsdetector -httpPort 8080 -ttl 300

Installation

1. Clone this repository:

git clone https://github.com/eltorio/public-dnsdetector.git

2. Set up your server environment (ensure ports 53 and 80 are accessible).

3. Customize the configuration as needed.

Metrics

Our application exposes two metrics for monitoring:

publicdns_detector_unique_ips_total

publicdns_detector_unique_ips_total is a metric that counts the total number of unique IP addresses that have made requests to our application. This metric can be useful for monitoring the diversity of clients that are using our service.

publicdns_detector_requests_total

publicdns_detector_requests_total is a metric that counts the total number of requests received by our application. This metric can be useful for monitoring the volume of traffic that our service is receiving.

Using the Metrics

These metrics are exposed at the /metrics endpoint of our application and are in a format compatible with Prometheus. Therefore, you can use them with any monitoring tool that supports Prometheus.

For example, to scrape these metrics with Prometheus, you can add the following to your Prometheus configuration:

scrape_configs:
    - job_name: 'publicdns_dector'
        static_configs:
            - targets: ['<publicdns_detector_host>:<publicdns_detector_port>']

Docker Deployment

Our application is available as a Docker image hosted at docker.io with the tag eltorio/publicdns-detector:latest.

To run the Docker image, you need to have Docker installed on your machine. Once Docker is installed, you can use the following command to run the image:

docker run -p 53:53/udp -p 80:80 eltorio/publicdns-detector:latest

License

This project is licensed under the GNU Affero General Public License v3.0. See the LICENSE file for details.

---

Feel free to modify and expand upon this template to provide additional details specific to your project. Good luck with your Public DNS Detector! 🚀