IPv4 has 4.3 billion addresses. We ran out years ago. IPv6 has 340 undecillion addresses (3.4×10^38). But we cannot switch overnight — billions of devices only speak IPv4. Transition mechanisms bridge this gap.
Dual Stack: The Ideal Solution
In a perfect world, every device runs both IPv4 and IPv6 simultaneously. The device prefers IPv6 when available and falls back to IPv4 otherwise.
Problem: Requires IPv6 support everywhere — ISP, router, and destination server. Many ISPs still do not offer IPv6.
6to4: Automatic Tunneling (Deprecated)
6to4 encapsulates IPv6 packets inside IPv4 packets. Your public IPv4 address is embedded in a special IPv6 prefix (2002::/16).
Issues: Relies on relay routers that may be unreliable or far away. Officially deprecated due to operational problems.
Teredo: IPv6 Through NAT
Teredo (Windows built-in) tunnels IPv6 over UDP port 3544, allowing it to traverse NAT. Used when no native IPv6 or 6to4 is available.
Performance is poor — multiple layers of encapsulation add latency. Microsoft Edge and Teams may use it if no better option exists.
NAT64 + DNS64: IPv6-Only Networks
Modern approach for new networks that are IPv6-only internally:
- DNS64: When an IPv6 client queries a domain that only has an A record (IPv4), DNS64 synthesizes a fake AAAA record pointing to a special prefix (64:ff9b::/96)
- NAT64: When packets arrive at the NAT64 gateway destined for 64:ff9b::/96, it translates them to IPv4 and forwards to the real server
Apple mandates that iOS apps work on IPv6-only networks with NAT64. This is why developers must not hardcode IPv4 addresses.
464XLAT: Client-Side Translation
For apps that absolutely require IPv4, 464XLAT adds another translation layer on the client device. Android uses this to run legacy apps on IPv6-only mobile networks.
Checking Your IPv6 Status
Visit our homepage — we show both your IPv4 and IPv6 addresses if available. You can also visit test-ipv6.com for a comprehensive connectivity test.