6to4
IPv6-over-IPv4-tunneling-mechanism. RFC 3056 (2002). Public-IPv4-address mappade automatic till IPv6-prefix 2002:WWXX:YYZZ::/48 (W.X.Y.Z är IPv4). Standard early-IPv6-deployment, deprecated 2015 pga reliability-issues.
Hur: client encapsulates IPv6-packets i IPv4, sends to nearest 6to4-relay (anycast 192.88.99.1). Relay decapsulates, forwards over native-IPv6. Problem: relay-quality varies wildly, asymmetric-routing common, debugging-nightmare. RFC 7526 (2015) deprecated 6to4 + 6rd. Modern alternative: native-IPv6 (most ISPs), Hurricane Electric tunnelbroker, WireGuard-IPv6-tunnels. Historic-legacy: many 2001-2010-era-blogs explained 6to4 as the IPv6-onramp; today mostly historic-curiosity.