It relies on underlying protocols to take care of this. Fragmentation only by source host - Intermediate and network fragmentation is no longer supported. Only the sending host can fragment packets. The sender therefore has to be able to do a reliable MTU path discovery and determine fragmentation needs himself. Extension headers - IPV6 is much more flexible in its support of options.
Options appear as extension headers that follow the IP header in the datagram.
Built in security - IPV6 requires support both for authentication and confidentiallity. Autoconfiguration - More and more users of the internet are not computer people and therefore have a difficult time setting up the machines. IPV6 allows autoconfiguration of the devices by either the router, DHCP server or both. Anycast - IPV6 does not contain a broadcast address, it instead uses a anycast address. If you send a packet to a anycast group, the router only has to make sure that it gets delivered to one of the addresses in that group.