Dynamic DNS (DDNS) automatically updates DNS records—typically A records or AAAA records—when the IP address bound to a hostname changes. This enables devices with constantly-changing IPs (like home routers or ISP-assigned addresses) to maintain a stable hostname for access.
How it works
When a client (router, host agent, or software) detects an IP address change, it sends an update to a DNS server using one of two methods:
- RFC 2136 DNS UPDATE — the client sends a dynamic update message directly to an authoritative nameserver that supports the protocol.
- Provider HTTP(S) API — most consumer DDNS services (routers, NAS devices) use a proprietary REST endpoint instead (e.g., a simple GET request).
The authoritative server updates the zone record; DDNS typically uses very low TTL values (60–300 seconds) so resolvers pick up changes quickly.
Updates can be authenticated using TSIG (Transaction Signature) — a shared-secret mechanism — to prevent unauthorized zone tampering.
Common use case
A home router with a dynamic ISP-assigned IP registers myhome.example.com with a DDNS provider. Each time the ISP reassigns a new IP, the router's DDNS client sends an automatic update, so the hostname always resolves to the current address—enabling remote access (VPN, IP camera, self-hosted service) without paying for a static IP.
WarningLow TTLs required for DDNS responsiveness conflict with DNS caching. Some resolvers, CDNs, or ISP DNS servers ignore or override low TTLs, causing stale IP resolution for minutes after a change. Free or dynamic subdomains are also frequently blocklisted by security policies and may be excluded from browser cookie rules.
Check your router or hosting provider's documentation to enable and configure DDNS for your specific service.