Differences between IPv4 and IPv6

IPv6 solves the Address Depletion Problem

With the explosion in the popularity of the Internet has come the introduction of commerce related activities that can now be done over the Internet by an ever-increasing number of devices. With IPv4, the number of public addresses available to new devices is limited and shrinking. IPv4 cannot continue to scale and provide global connectivity to all of the planned Internet-capable devices to be produced and connected in the next 10 years. Although these devices can be assigned private addresses, address and port translation introduces complexity to the devices that want to perform server, listening, or peer functionality. IPv6 solves the IPv4 public address depletion problem by providing an address space to last well into the twenty-first century. The business benefit of moving to IPv6 is that mobile cell phones, personal data assistants (PDAs), automobiles, appliances, and even people can be assigned multiple globally reachable addresses. The growth of the devices connected to the Internet and the software that these devices run can proceed without restraint and without the complexity and cost of having to operate behind NATs.

IPv6 Solves the Disjoint Address Space Problem

With IPv4, there are typically two different addressing schemes for the home and the enterprise network.
In the home, an Internet gateway device (IGD) is assigned a single public IPv4 address and the IGD assigns private IPv4 addresses to the hosts on the home network.
An enterprise might have multiple public IPv4 addresses or a public address range and either assign public, private, or both types of addresses within the enterprise’s intranet.
However, the public and private IPv4 address spaces are disjoint; they do not provide symmetric reach ability at the Network layer. Symmetric reach ability exists when packets can be sent to and received from an arbitrary destination. With IPv4, there is no single addressing scheme that is applied to both networks that allows seamless connectivity. Connectivity between disjoint networks requires intermediate devices such as NATs or proxy servers. With IPv6, both homes and enterprises will be assigned global address prefixes and can seamlessly connect, subject to security restrictions such as firewall filtering and authenticated communication.

IPv6 Solves the International Address Allocation Problem

The Internet was principally a creation of educational institutions and government agencies of the United States of America. In the early days of the Internet, connected sites in the United States received IPv4 address prefixes without regard to summarize ability or need. The historical result of this address allocation practice is that the United States has a disproportionate number of public IPv4 addresses.
With IPv6, public address prefixes are assigned to regional Internet registries, which, in turn, assign address prefixes to other ISPs and organizations based on justified need. This new address allocation practice ensures that address prefixes will be distributed globally based on regional connectivity needs, rather than by historical origin. This makes the Internet more of a truly global resource, rather than a United States—centric one. The business benefit to organizations across the globe is that they can rely on having available public IPv6 address space, without the current cost of obtaining IPv4 public address prefixes from their ISP.

IPv6 Restores End-to-End Communication

With IPv4 NATs, there is a technical barrier for applications that rely on listening or peer based connectivity because of the need for the communicating peers to discover and advertise their public IPv4 addresses and ports. The workarounds for the translation barrier might also require the deployment of echo or rendezvous servers on the Internet to provide public address and port configuration information.
With IPv6, NATs are no longer necessary to conserve public address space, and the problems associated with mapping addresses and ports disappear for developers of applications and gateways. More importantly, end-to-end communication is restored between hosts on the Internet by using addresses in packets that do not change in transit.

IPv6 Uses Scoped Addresses and Address Selection

Unlike IPv4 addresses, IPv6 addresses have a scope, or a defined area of the network over which they are unique and relevant. For example,
IPv6 has a global address that is equivalent to the IPv4 public address and a unique local address that is roughly equivalent to the IPv4 private address.
Typical IPv4 routers do not distinguish a public address from a private address and will forward a privately addressed packet on the Internet.
An IPv6 router, on the other hand, is aware of the scope of IPv6 addresses and will never forward a packet over an interface that does not have the correct scope.

IPv6 Has More Efficient Forwarding

IPv6 is a streamlined version of IPv4. Excluding prioritized delivery traffic, IPv6 has fewer fields to process and fewer decisions to make in forwarding an IPv6 packet.
Unlike IPv4, the IPv6 header is a fixed size (40 bytes), which allows routers to process IPv6 packets faster. Additionally, the hierarchical and summarize able addressing structure of IPv6 global addresses means that there are fewer routes to analyze in the routing tables of organization and Internet backbone routers. The consequence is traffic that can be forwarded at higher data rates, resulting in higher performance for tomorrow’s high-bandwidth applications that use multiple data types.

IPv6 Has Support for Security and Mobility

IPv6 has been designed to support security (IPsec) (AH and ESP header support required) and mobility (Mobile IPv6) (optional). Although one could argue that these features are available for IPv4, they are available on IPv4 as extensions, and therefore they have architectural or connectivity limitations that might not have been present if they had been part of the original IPv4 design. It is always better to design features in rather than bolt them on. The result of designing IPv6 with security and mobility in mind is an implementation that is a defined standard, has fewer limitations, and is more robust and scalable to handle the current and future communication needs of the users of the Internet. The business benefit of requiring support for IPsec and using a single, global address space is that IPv6 can protect packets from end to end across the entire IPv6 Internet. Unlike IPsec on the IPv4 Internet, which must be modified and has limited functionality when the endpoints are behind NATs, IPsec on the IPv6 Internet is fully functional between any two endpoints.