IPv6

Internet Protocol Version 4 is the most popular protocol in use today, although there are some questions about its capability to serve the Internet community much longer. IPv4 was finished in the 1970s and has started to show its age. The main issue surrounding IPv6 is addressing-or, the lack of addressing-because many experts believe that we are nearly out of the four billion addresses available in IPv4. Although this seems like a very large number of addresses, multiple large blocks are given to government agencies and large organizations. IPv6 could be the solution to many problems,

Many of the finest developers and engineering minds have been working on IPv6 since the early 1990s. Hundreds of RFCs have been written and have detailed some major areas, including expanded addressing, simplified header format, flow labeling, authentication, and privacy.

Expanded addressing moves us from 32-bit address to a 128-bit addressing method. It also provides newer unicast and broadcasting methods, injects hexadecimal into the IP address, and moves from using "." to using ":" as delimiters.

Differences Between IPv4 and IPv6

IPv4	IPv6
Source and destination addresses are 32 bits (4 bytes) in length.	Source and destination addresses are 128 bits (16 bytes) in length. For more information, see “IPv6 Addressing.”
IPsec support is optional.	IPsec support is required. For more information, see “IPv6 Header.”
No identification of packet flow for QoS handling by routers is present within the IPv4 header.	Packet flow identification for QoS handling by routers is included in the IPv6 header using the Flow Label field. For more information, see “IPv6 Header.”
Fragmentation is done by both routers and the sending host.	Fragmentation is not done by routers, only by the sending host. For more information, see “IPv6 Header.”
Header includes a checksum.	Header does not include a checksum. For more information, see “IPv6 Header.”
Header includes options.	All optional data is moved to IPv6 extension headers. For more information, see “IPv6 Header.”
Address Resolution Protocol (ARP) uses broadcast ARP Request frames to resolve an IPv4 address to a link layer address.	ARP Request frames are replaced with multicast Neighbor Solicitation messages. For more information, see “Neighbor Discovery.”
Internet Group Management Protocol (IGMP) is used to manage local subnet group membership.	IGMP is replaced with Multicast Listener Discovery (MLD) messages. For more information, see “Multicast Listener Discovery.”
ICMP Router Discovery is used to determine the IPv4 address of the best default gateway and is optional.	ICMP Router Discovery is replaced with ICMPv6 Router Solicitation and Router Advertisement messages and is required. For more information, see “Neighbor Discovery.”
Broadcast addresses are used to send traffic to all nodes on a subnet.	There are no IPv6 broadcast addresses. Instead, a link-local scope all-nodes multicast address is used. For more information, see “Multicast IPv6 Addresses.”
Must be configured either manually or through DHCP.	Does not require manual configuration or DHCP. For more information, see “Address Autoconfiguration.”
Uses host address (A) resource records in the Domain Name System (DNS) to map host names to IPv4 addresses.	Uses host address (AAAA) resource records in the Domain Name System (DNS) to map host names to IPv6 addresses. For more information, see “IPv6 and DNS.”
Uses pointer (PTR) resource records in the IN-ADDR.ARPA DNS domain to map IPv4 addresses to host names.	Uses pointer (PTR) resource records in the IP6.ARPA DNS domain to map IPv6 addresses to host names. For more information, see “IPv6 and DNS.”
Must support a 576-byte packet size (possibly fragmented).	Must support a 1280-byte packet size (without fragmentation). For more information, see “IPv6 MTU.”

More Reference :-http://en.wikipedia.org/wiki/IPv6