What is IPv6?
The successor to IPv4, using 128-bit addresses to provide a vastly larger address space and a few protocol simplifications.
IPv6 was designed in the 1990s once it became clear IPv4 would run out of addresses. A v6 address looks like 2001:0db8:85a3:0000:0000:8a2e:0370:7334, which collapses with double-colon shorthand to 2001:db8:85a3::8a2e:370:7334. The address space is 2^128, enough to assign trillions of addresses per square millimeter of Earth.
Beyond size, IPv6 cleans up several IPv4 quirks. There is no NAT in the v6 model: every device gets a globally routable address. Header processing is simpler and fragmentation is handled by the sender rather than routers. Stateless address autoconfiguration (SLAAC) lets devices generate their own addresses from a router prefix without a DHCP server.
Adoption is uneven. Mobile networks in the US and India are mostly v6; many enterprise and small-business networks are still v4-only. For crawlers, the practical impact is that a v6-only target requires v6-capable proxies, and IP-based rate limiting on v6 has to be by /64 prefix rather than per address (since one device can trivially rotate within its /64).
In the wild
- A T-Mobile phone connecting to youtube.com over IPv6 with a v4 fallback for legacy services
- A data center scraper using a /64 prefix to rotate IPs without buying a new proxy
- A geolocation database tagging a /48 v6 prefix with a city since v6 is allocated more granularly than v4