Capabilities of IPv6

The basic carriage and management services of IPv4 all have their equivalents in IPv6. However IPv6 offers enhanced and additional capabilities:

Vastly Increased Address Space

Extending the 4 billion IPv4 addresses to the 340 trillion trillion trillion IPv6 addresses allows all existing network devices to receive addresses. It also allows almost any conceivable number of new devices and applications to be separately, globally and uniquely addressed. Consider the millions of mobile phones in the world, the millions of cars – and each car has about 200 addressable processes. A single home could potentially have thousands of addressable items in it.

Fixed 40-byte Headers

IPv4 packet headers vary in size depending on the attributes assigned. IPv6 headers are a fixed 40 bytes in size. IPv6 routing devices can be thus be optimised to deliver increased packet forwarding rates (a 12% to 15% improvement in some cases).


Autoconfiguration is the automatic configuration of devices without manual intervention. When an IPv6 network adapter is activated, it assigns itself an IP address based on a standard prefix and its own MAC address. It can then communicate on the local network to obtain globally routable addresses, gateway addresses, security settings, policy attributes and so on.

IPsec Support

IPv4 was developed at a time when security was not a major concern. Authenticating protocols such as IPsec were developed later and need to be retrofitted to IPv4. This leads to interoperability and implementation inconsistencies. IPv6, on the other hand, has security as a major design criteria. A conforming standards based IPv6 protocol stack has IPsec support. While it may not be used, it is there.

End-to-end Transparency

Network Address Translation (NAT), developed as a technical fix to a looming IPv4 address shortage, has an unfortunate side-effect - it breaks the end-to-end transparency that was a hallmark of early IPv4 services. The NAT devices in most of today's Internet connections prevent visibility between end users. Among other things, this makes end-to-end encryption difficult. It also makes it harder for end users to deliver content - they can only consume. IPv6, by restoring end-to-end transparency, removes these difficulties.

Attribute Extension Headers

To conserve space in the IPv6 packet header, a series of Extension Attribute packets have been defined. Instead of burdening the main packet header with security, Quality of Service, encryption, performance and management payloads, these have been assigned their own unique packet structures. If they are needed, they are inserted between the routing header and the payload. The routing header includes an indication as to the presence of Extended Attribute packets. This vastly speeds up the router packet forwarding rates and improves efficiency.


Anycast addressing, unique to IPv6, refers to a single source contacting a predetermined list of destinations, of which only one responds and participates in subsequent transmissions. The other anycast destinations realise that one has responded and do not participate further or are ignored.

Anycasting has many applications including the distribution of multimedia and video over the Internet. For example, a customer might request a video package from a news server and the geographically closest, topologically closest, least loaded or least expensive server may respond. There are many Anycast possibilities and most have not yet been explored or exploited.

Anycasting with IPv4 is not done in the protocol or on participating hosts, but instead by configuring multiple routes in the network; it is far less flexible and far less useful.


When a device moves from its home network, its IP address will be recognised as a foreign address in its new location and will be denied service. The gateway it originally was told to use in its home network is no longer valid and communication sessions will not be established. This may happen many times in the course of a single journey, across a city for example, where many different carrier services might need to be utilised.

To overcome this limitation, a process called MobileIP was developed in IPv4. This consisted of the devices calling 'home' and telling the home network of its changing gateway environments (the foreign correspondent model). This is a very inefficient way to operate as all traffic to and from the mobile device has to be routed via the home network.

MobileIP has been extended in IPv6 to overcome this inefficient triangulation. In MobileIPv6, a foreign correspondent server is continuously updated as to the network the device is in and which gateway to use to reach the traveling device. The bulk of the packets flow directly between mobile device and its communicators, and not via the home address. This reduces cost and vastly improves performance and reliability.

Flow Label QoS

All of the Differentiated Services (DiffServ) and Integrated Services (IntServ) Quality of Service attributes from IPv4 are preserved in IPv6. In addition, unique to IPv6, is the 20 byte Flow Label field. This field is being developed to provide a rich set of Quality of Service attributes for the growing IPv6 world.