What is IPv6

The IETF identified the problem with the rapid exhaustion of the IPv4 address space several decades ago. Despite the invention of classless IP addressing, it was assessed that a new addressing protocol was required to address long term needs. IPv6 was then designed as the succeeding standard to IPv4 and released in 1995. The resulting address space was then increased from 32 to 128 bits (16 octets) and deemed to be adequate for at least the mid-term requirements for Internet growth. The design of IPv6 incorporates the idea of allowing efficient aggregation of subnet routing prefix at the router level. This results in the reduction of routing table sizes and actual address utilization rates being small on any IPv6 network segment. The design also allows for the separation of the addressing infrastructure of a local segment’s space from the addressing used to route to or from external network traffic. The large number of network addresses also allows large blocks to be assigned for a specific purpose and when required aggregated for more efficient routing. The need for more complicated addressing conservation methods such as now used in Classless Inter-Domain Routing (CIDR) is also eliminated with the implementation of IPv6.
Similar to IPv4, IPv6 reserves blocks of IP address for private use. In IPv6; however, these are referred to as unique local addresses (ULA). This block of addresses uses the routing prefix fc00::/7 that is then divided into two /8 blocks that have different implied policies. The addresses include a 40-bit pseudorandom number which minimizes the risk of address collisions if packets are routed inappropriately or sites merge. None of the current or legacy IPv6 private address prefixes are supposed to be routed on the public Internet just like the behavior expected from IPv5. Finally, despite the majority of modern operating systems now providing support for IPv6, it has not yet seen widespread deployment in the home networking, VoIP, and networking peripheral fields.

What is an IP Address?

An Internet Protocol (IP) address is a numeric label consisting of a 32 bit number assigned to a network capable device that uses IP for communication. The address fundamentally serves two purposes: location addressing and computer host or network interface identification. The address indicates where the connected device resides with the majority of hosts/devices still using the IPv4 (Internet Protocol Version 4) form of addressing. A significant limitation of the legacy IPv4 addressing is that it supports less than 4.3 billion total addresses. Based on the rapid growth of the Internet and related technologies, the use of IPv4 is not sustainable for the long term. In the mid-1990’s, the new IPv6 technique was developed which makes use of 128 bits for the IP address. IPv6 technology continues to be deployed, albeit slowly. The Internet Assigned Numbers Authority (IANA) is responsible under the IETF for management of the IP address space allocation globally. Beneath the IANA, there are five regional Internet registries (RIRs) that are responsible for allocating IP address blocks to Internet service providers (ISPs) and other trusted organizations.

IP address classes

There were five IP address classes in use before the majority of industry switched to classless routing. There were A, B, C, D, and E. Class A addresses were used for networks with a very large number of total hosts. Class B was designed for use on medium to large networks, and C for small local area networks (LANs). Class D and E were set aside for multicast and experimental purposes. In the following table, the four octets that make up an IP address (a, b, c, and d respectfully) are displayed in how they were distributed in classes A, B, and C. classes A, B, and C.

Class	1st Octet Decimal Range	1st Octet High Order Bits	Network/Host ID (N=Network, H=Host)	Default Subnet Mask	Number of Networks	Hosts per Network (Usable Addresses)
A	1 – 126*	0	N.H.H.H	255.0.0.0	126 (27 – 2)	16,777,214 (224 – 2)
B	128 – 191	10	N.N.H.H	255.255.0.0	16,382 (214 – 2)	65,534 (216 – 2)
C	192 – 223	110	N.N.N.H	255.255.255.0	2,097,150 (221 – 2)	254 (28 – 2)
D	224 – 239	1110	Reserved for Multicasting
E	240 – 254	1111	Experimental; used for research