Larger Address Space
Compare to IPv4, IPv6 increases the number of address bits by a factor of 4, from 32 bits to 128 bits. Studies conducted sat the 128 bits IPv6 address will lead to aproximately 1000 address per person on this planet.

Simplified Header Format
The IPV4 header fields Header Legth (IHL), identification, Flags, Fragment offset, header checksum, and padding fields have been removed in IPv6. This removal results in faster processing of the basic IPv6 header.
The options field of IPv4 is changed in IPv6 and is now managed by an extention header chain. The majority of the other fields were either not changed or changed only slightly. In addition to a smaller number of fields, the header is 64 bits aligned to enable fast processing by current processors.

Hierarchical Network Structure
in IPv6, hierarchical addressing is used to optimise routing and improve the efficiency of the network. A basic IPv6 principle is the minimal processing routers along the way should do. The IANA allocates each regional internet registry or RIR a number of prefixes to fulfill their needs. RIR`s then allocate smaller prefixes to the LIR`s that in turn allocate prefices to their customers. All IPv6 prefixes then, are provider asigned. Contrary to what exists for IPv4, Independent, are not provided.

Mandatory IPsec Implementation
IPSec is the P security architecture that can protect all IP protocol communication. IPsec is designed for both
IPv4 and IPv6. If its implementation  is optional in IPvr, its mandatory in IPv6. All full IPv6 implemantations have to support IPSec.

Multicast not Broadcast
Transmissions addressed simultaneously to more then one system, can be broadcast or multicasts. Broadcast are used when a piece of information needs communicating to everyone on the network or when the sender does not know the exact location of the system it want to cummunicate with. The exact notation of a broadcast address can vary by the operating system, but it is identified with all 1`s as the host section of an IPv4 address. Each broadcast message causes a CPU interupt on a host that receives such message. Multicast improves the efficiency of a network by limiting the broadcast request to smaller number of only
interested nodes. Hence, it provides less CPU interrupts for the hosts on a network segment. in IPv6, the functions previously supported by IPv4 broadcast such as ARP have been redesigned as router discovery and router soliciation request and are handled by IPv6 multicast. Multicast allows IP packets such as a video stream to be sent to multiple destinations at the same time saving network bandwith. IPv6 uses spesific multicast group address for it uses spesific multicast group addresses for its various function. Thus, Pv6 multicast prevents the problems causes by broadcast storms in IPv4 network.

ICMP
For IPv4, the internet control message protocol, is an internet protocol that is used for reporting fault and
information conditions and for diagnostic functions. It provides error correction and other information relevant to IP packet processing. For example, it can let the IP software on one machine inform another machine about an unreachable destination.

source : http://www.6diss.org/