dnsv4

README

dnsv4

A DNS proxy server that prioritizes IPv4 over IPv6 connections while maintaining IPv6 fallback support. This helps prevent connectivity issues in environments where IPv6 may be unreliable or slower than IPv4.

Purpose

dnsv4 is designed to optimize connectivity by prioritizing IPv4 over IPv6 while still allowing IPv6 fallback. It does this by:

• When a client requests an AAAA (IPv6) record, dnsv4 first checks if an A (IPv4) record exists
• If an IPv4 record exists, the AAAA query returns empty (suppressing IPv6)
• If no IPv4 record exists, the AAAA query proceeds normally, allowing IPv6 connectivity

This approach ensures:

• Applications will try IPv4 first when both are available
• IPv6 still works for domains that are IPv6-only
• Better reliability in environments with problematic IPv6 connectivity
• Faster connections by avoiding IPv6 timeout delays when IPv4 is available

Prerequisites

Go 1.18 or higher github.com/miekg/dns package

Installation

Clone the repository:

git clone https://github.com/cmspam/dnsv4
cd dnsv4
Install dependencies:
go mod init dnsv4
go get github.com/miekg/dns
Build the binary:
go build

Configuration

dnsv4 can be configured through command-line flags or a JSON configuration file. Command Line Options

-listen: Address and port to listen on (default: "127.0.0.1:53")
-upstream: Upstream DNS server address and port (default: "1.1.1.1:53")
-proxy-only: Disable IPv4 prioritization (default: false)
-config: Path to configuration file

Configuration File

Create a JSON file (e.g., config.json):

{
    "upstream": "1.1.1.1:53",
    "listen": "127.0.0.1:53",
    "proxy_only": false
}

Usage

Basic usage with defaults: sudo ./dnsv4

Using command line options:

sudo ./dnsv4 -upstream "8.8.8.8:53" -listen "0.0.0.0:5353"

Using a config file:

sudo ./dnsv4 -config config.json

Enable proxy-only mode (disable IPv4 prioritization):

sudo ./dnsv4 -proxy-only

Note: Running on port 53 requires root/administrator privileges The default configuration:

• Listens on 127.0.0.1:53
• Uses Cloudflare's DNS (1.1.1.1:53) as upstream server
• IPv4 prioritization enabled

How It Works

For regular DNS queries (A records, MX records, etc.), dnsv4 acts as a transparent proxy For AAAA (IPv6) queries (when not in proxy-only mode):

• First checks if an A record exists for the domain
• If an A record exists, returns an empty success response
• If no A record exists, proxies the AAAA query to get IPv6 records

In proxy-only mode, all queries are forwarded to the upstream server without modification

Testing You can test the DNS server using dig or nslookup:

Test IPv4 prioritization (when not in proxy-only mode)

dig @127.0.0.1 example.com AAAA # Should return empty if A record exists

Test IPv6 fallback

dig @127.0.0.1 ipv6.google.com AAAA # Should return IPv6 if no A record

Test regular IPv4 resolution

dig @127.0.0.1 example.com A

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.