While IPv6 has been around since 1998, global adoption still sits at around 40% according to Google's statistics. Major tech companies like Facebook and Google have enabled IPv6-only access, but many ISPs and mobile networks still rely heavily on IPv4. This creates a compatibility dilemma for server administrators.

For production web servers, I strongly recommend implementing dual stack (both IPv4 and IPv6) rather than IPv6-only. Here's why:

• Ensures maximum compatibility with all client devices
• Prevents potential loss of traffic from IPv4-only networks
• Maintains SEO rankings (some crawlers still IPv4-only)
• Prepares for future IPv6 transition

Here's how to properly configure Nginx for dual stack:

server {
    listen 80;
    listen [::]:80 ipv6only=on;
    
    listen 443 ssl;
    listen [::]:443 ssl ipv6only=on;
    
    server_name example.com;
    # Rest of your configuration...
}

The ipv6only=on parameter prevents binding issues on dual-stack systems.

Use these commands to verify your setup:

# Check IPv4
curl -4 http://example.com
# Check IPv6 
curl -6 http://example.com
# Check DNS records
dig A example.com +short
dig AAAA example.com +short

Dual stack adds minimal overhead:

• Memory usage increase: ~1-2% per connection
• CPU impact: Negligible for most workloads
• Network throughput: Identical for both protocols

When you're ready to transition:

1. Monitor IPv6 traffic percentage (should be >95%)
2. Implement 464XLAT for IPv4 fallback
3. Update DNS to IPv6-only with synthetic records

While IPv6 adoption has been steadily growing (reaching about 40% globally according to Google statistics), the internet still largely runs on IPv4. Major cloud providers like AWS, Google Cloud, and Linode now offer native IPv6 support, but many ISPs and corporate networks still rely solely on IPv4.

The most robust solution is to configure your Nginx server with dual-stack support. This ensures maximum compatibility while future-proofing your setup. Here's why:

• Guaranteed accessibility for all users regardless of their network capabilities
• No DNS resolution issues (AAAA records won't work for IPv4-only clients)
• Better performance through native IPv6 connectivity where available
• Compliance with modern web standards and best practices

Here's a proper dual-stack Nginx configuration for Ubuntu:

server {
    listen 80;
    listen [::]:80;
    
    listen 443 ssl;
    listen [::]:443 ssl;
    
    server_name example.com www.example.com;
    
    # SSL configuration would go here
    # ...
    
    root /var/www/html;
    index index.html;
}

After implementing dual-stack, verify it works correctly:

# Check IPv4 connectivity
curl -4 http://example.com

# Check IPv6 connectivity
curl -6 http://example.com

# View listening ports
ss -tulnp | grep nginx

Contrary to some beliefs, running dual-stack doesn't significantly impact performance. The Linux kernel handles IPv4 and IPv6 efficiently:

• Memory overhead is minimal (about 1KB per connection)
• CPU usage difference is negligible for modern processors
• Network latency is protocol-independent

When transitioning from IPv4-only to dual-stack:

1. Ensure your DNS has both A and AAAA records
2. Test with real users across different networks
3. Monitor IPv6 traffic using analytics tools
4. Consider implementing Happy Eyeballs for optimal connection handling

In very specific cases, IPv6-only might be appropriate:

• Internal services in IPv6-only networks
• Specialized applications targeting mobile networks (where IPv6 penetration is high)
• When using NAT64/DNS64 translation services