IPV6

                                                   ***  IPv6 Addressing  ***

IPv6 Basics

The most widespread implementation of IP currently is IPv4, which utilizes 

a 32-bit address. Mathematically, a 32-bit address can provide roughly 4 

billion unique IP addresses (232= 4,294,967,296). Practically, the number of 

usable IPv4 addresses is much lower, as many addresses are reserved for 

diagnostic, experimental, or multicast purposes. 

The explosive growth of the Internet and corporate networks quickly led to 

an IPv4 address shortage. Various solutions were developed to alleviate this 

shortage, including CIDR, NAT, and Private Addressing. However, these 

solutions could only serve as temporary fixes. 

In response to the address shortage, IPv6 was developed. IPv6 increases the 

address size to 128 bits, providing a nearly unlimited supply of addresses 

(340,282,366,920,938,463,463,374,607,431,768,211,456 to be exact). This 

provides roughly 50 octillion addresses per person alive on Earth today, or 

roughly 3.7 x 1021 addresses per square inch of the Earth’s surface.

IPv6 offers the following features: 

• Increased Address Space and Scalability – providing the absurd

number of possible addresses stated previously.

• Simplified Configuration – allows hosts to auto-configure their IPv6

addresses, based on network prefixes advertised by routers.

• Integrated Security – provides built-in authentication and encryption

into the IPv6 network header

• Compatibility with IPv4 – simplifies address migration, as IPv6 is

backward-compatible with IPv4

The IPv6 Address

The IPv6 address is 128 bits, as opposed to the 32-bit IPv4 address. Also

unlike IPv4, the IPv6 address is represented in hexadecimal notation,

separate by colons.

An example of an IPv6 address would be:

1254:1532:26B1:CC14:0123:1111:2222:3333

Each “grouping” (from here on called fields) of hexadecimal digits is 16

bits, with a total of eight fields. The hexadecimal values of an IPv6 address

are not case-sensitive.

We can drop any leading zeros in each field of an IPv6 address. For

example, consider the following address:

1423:0021:0C13:CC1E:3142:0001:2222:3333

We can condense that address to: 1423:21:C13:CC1E:3142:1:2222:3333

Only leading zeros can be condensed. If we have an entire field comprised of

zeros, we can further compact the following address:

F12F:0000:0000:CC1E:2412:1111:2222:3333

The condensed address would be: F12F::CC1E:2412:1111:2222:3333

Notice the double colons (::). We can only condense one set of contiguous

zero fields. Thus, if we had the following address:

F12F:0000:0000:CC1E:2412:0000:0000:3333

We could not condense that to: F12F::CC1E:2412::3333

The address would now be ambiguous, as we wouldn’t know

The IPv6 Address Hierarchy

IPv4 separated its address space into specific classes. The class of an IPv4

address was identified by the high-order bits of the first octet:

• Class A - (00000001 – 01111111, or 1 - 127)

• Class B - (10000000 – 10111111, or 128 - 191)

• Class C - (11000000 – 11011111, or 192 - 223)

• Class D - (11100000 – 11101111, or 224 - 239)

IPv6’s addressing structure is far more scalable. Less than 20% of the IPv6

address space has been designated for use, currently. The potential for

growth is enormous.

The address space that has been allocated is organized into several types,

determined by the high-order bits of the first field:

• Special Addresses – addresses begin 00xx:

• Link Local – addresses begin FE8x:

• Site Local – addresses begin FECx:

• Aggregate Global – addresses begin 2xxx: or 3xxx:

• Multicasts – addresses begin FFxx:

• Anycasts