Dynamic DNS (DDNS) is essential for maintaining a stable name for your home network, even when your Internet Service Provider (ISP) assigns you a dynamic public IP address that frequently changes. This doc explains what DDNS is, how it works, the different options available, and some common pitfalls.
What is Dynamic DNS?
The problem with dynamic IPs is that they change periodically—due to router restarts, lease renewals, or ISP whims. Any service relying on a static IP address (like a DNS record, a VPN client configuration, or a bookmarked camera page) will break when the IP changes. DDNS addresses this issue by using a domain name that automatically updates with your current public IP.
How Does Dynamic DNS Work?
DDNS works through an updater script or application that runs on a device always connected to the internet (like a router, NAS, or another always-on computer). This updater periodically checks your current public IP address and, when it changes, updates the corresponding DNS record with the provider's API. The result is that your domain name reflects your current public IP within seconds to minutes.
To ensure quick updates, the DNS record typically has a low Time-To-Live (TTL) value—usually between 60 and 300 seconds. This setting ensures that DNS caches expire quickly, making sure that your domain name points to the correct IP address as soon as it changes.
Options for Dynamic DNS
Your Own Domain + API-Updatable DNS
- Cloudflare: The most reliable option where you use Cloudflare's API to keep your own domain current. This method is ideal for serious users and businesses.
- Pros: No additional costs beyond the domain, flexible with various scripts or tools like
ddclient,inadyn, or a simple 5-line cron script.
- Pros: No additional costs beyond the domain, flexible with various scripts or tools like
- Router Built-Ins: Most modern routers offer built-in DDNS support for popular providers. This is the easiest setup but may not be as customizable.
- Pros: Zero maintenance, always up-to-date with your WAN IP.
Free DDNS Providers
- DuckDNS, Dynu, and No-IP
- Pros: Easy to set up and use for personal projects or small-scale applications. DuckDNS is particularly user-friendly.
- Cons: May require frequent confirmation clicks, which can be annoying but are necessary for free services.
Common Pitfalls
CGNAT (Carrier-Grade NAT)
For users behind CGNAT, DDNS can be less useful because the name will track an address that you cannot reach from the outside. In such cases, it's better to use tunnels or relay services instead of relying on direct IP access.
Updater Detection
Ensure your updater script checks the public IP from the internet rather than trusting a local network interface, which might be behind another NAT layer and give a different address.
TTL Settings
Avoid setting the TTL below 60 seconds. While it seems to speed up updates, most DNS providers ignore low TTLs, and resolvers may penalize such settings by not caching your domain for long periods.
Modern Alternatives
For those who expose services via tunnels (like Cloudflare or Tailscale), DDNS becomes less critical because the tunnel handles connectivity regardless of the public IP. However, DDNS remains useful for direct UDP-based services like WireGuard endpoints or game servers that require a real IP address.
By understanding these concepts and options, you can ensure your home network remains accessible even when your ISP assigns a dynamic IP address.