IPv6 Key Features Not In IPv4
Efficient and Extensible IP datagram
Efficient Route Computation and Aggregation
Improved Host and Router Neighbor Discovery
Required New Stateless and Stateful Address Autoconfiguration
Required Security for IP datagrams
Enhancements for Quality of Service and Differential Services
Enhancements for Mobile Networking
Enhancements for Dynamic Renumbering of Networks
Enhancements to avoid Congestion on the Internet