IPv6: a primer: an introduction to IPv6.

AuthorBarker, David
PositionNEW WHITE PAPER - Internet protocol


This paper looks at the evolution of the Internet Protocol (l) version 4 (IPv4) into version 6 (IPv6). It includes an introduction to IPv6, an overview of the limitations of IPv4, IPv6 features, key differences between the two protocols and the driving forces behind the need for transition. With World IPv6 day passing on the 6th June 2012 this paper is aimed at anyone who wants to understand how IPv6 works and why IPv4 needs to be replaced.

The Limitations of IPv4

The current version of IPv4 has not changed substantially in the past 30 years, since its publication in September 1981. During this lifespan IPv4 has proven to be robust, easily implemented and for the most part scalable enough (by utilising technologies such as Network Address Translation (NAT)), so that a move to IPv6 hasn't been necessary.

However the continued rise of internet connected devices over the past ten years and the evolving requirements for security of data transfer have now out-stripped the capabilities of IPv4.

The main limitations of IPv4 that have been become more apparent over the last few years are as follows:

* Insufficient IP address space

With only 32-bit capacity (4.2 billion unique addresses), IPv4 addresses have become relatively scarce, forcing a lot organisations to use NAT to map multiple private addresses to a single public IP address. While NAT promotes conservation of the public address space, it does not support standards-based network layer security or the correct mapping of all higher layer protocols. This can create problems when connecting two organisations that use the same private address space. The continued expansion of internet-connected devices and appliances is putting ever-increasing pressure on the public IPv4 address space.

* Address prefix allocation

Due to the way that IPv4 address prefixes have been (and continue to be) allocated, internet backbone routers are routinely required to maintain unreasonably large routing tables. The current routing table, as of October 2011, is just over 380,000 routes. This is up from 200,000 in 2007 and there are currently 5,000 new routing entries being added each month. The expansion of the global routing table, usually requiring multiple copies to be held when multi-homing tier-I carriers, has put pressure on memory requirements for existing routers as well as becoming increasingly complex for network administrators to maintain. The current IPv4 Internet routing infrastructure is a combination of both flat and hierarchical routing.

* Complexity of configuration

Most current IPv4 implementations must be either manually configured or use a stateful address configuration protocol such as Dynamic Host Configuration Protocol (DHCP). With more computers and devices using IP, there is a need for a simpler and more automatic configuration of addresses along with other configuration settings that do not rely on the administration of a DHCP infrastructure.

* Data security

Private communication, especially over a public medium like the internet, requires encryption services that protect the data being sent from being viewed or modified in transit. Although an add-on standard now exists for providing security on IPv4 packets (known as Internet Protocol Security or IPsec), this is optional and proprietary alternatives are commonly used.

* Quality of Service (QoS)

While standards for QoS exist for IPv4, no identification of packet flow for QoS handling by routers is present within the IPv4 header. Instead, real-time traffic support relies on the IPv4 Type of Service (ToS) field and the identification of the payload, typically using a UDP (User Datagram Protocol) or TCP (Transmission Control Protocol) port. However, the IPv4 ToS field has limited functionality and payload identification using a TCP or UDP port is not possible when the IPv4 packet payload is encrypted meaning traffic over a secure VPN (Virtual Private Network) connection can't be subjected to QoS policies.

IPv6, previously known as "IP-The Next Generation", was developed to address these limitations; it was specifically designed to minimise the impact upon the upper and lower layer protocols by standardising on packet head formation making it easier to handle new data types without affecting network performance.

The features of Ipv6


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