IPv4 and IPv6 Fundamentals 2.6

IP version 4 (IPv4) is one of the most popular protocols globally and is the primary traditional method for network communication.
Internet Protocol (IP) communication requires knowledge of both the current standard, IPv4, and the more recent standard, IPv6.
While IPv4 and IPv6 share operational similarities, they feature significant differences in their visual representation and system configuration.

IPv4 uses a $32$ -bit address, meaning it consists of $32$ ones and zeros working together to form a unique identifier.
To make it easier for humans to read, IPv4 is represented in decimal form as four separate decimal numbers separated by periods.
An example of an IPv4 address is $192.168.1.131$ .
The address is composed of four sections known as octets.
Each octet represents $8$ bits, which is also referred to as a byte.
The total length is $32$ bits, equivalent to $4$ bytes ( $4 \times 8 = 32$ ).
Each individual octet can consist of any value between $0$ and $255$ . An octet will never exceed the value of $255$ .

Communication across the public internet requires every connected device to have a unique IP address to differentiate itself from others (e.g., device $1.1.1.1$ communicating with device $2.2.2.2$ ).
The $32$ -bit architecture limits the total number of unique IPv4 addresses to approximately $4.29$ billion combinations ( $2^{32}$ ).
Currently, there are over $20$ billion devices connected to the internet, and this number is growing rapidly.
Because there are only $4.29$ billion addresses available for $20$ billion devices, specific technologies are required to enable communication for all devices.

One of the primary solutions to address exhaustion is Network Address Translation (NAT).
NAT allows a private network to use a single public IPv4 address to represent hundreds or thousands of internal devices.
Public addresses communicate with other public addresses on the internet.
Private addresses allow internal communication within a private network but do not count toward the global pool of $4.29$ billion IPv4 addresses.
A company might have a single link to the internet with one public IP, while using thousands of private addresses internally for internal hosts.

The ranges of private addresses are defined in RFC 1918. RFC stands for Request For Comment, representing the global standard for IPv4 private addressing.
There are three specific ranges defined for private network use:
- Range 1: $10.0.0.0$ through $10.255.255.255$ . This range provides over $16$ million addresses and is popular for large corporate networks.
- Range 2: $172.16.0.0$ through $172.31.255.255$ . This range provides just over $1$ million private addresses.
- Range 3: $192.168.0.0$ through $192.168.255.255$ . This range provides just over $65,000$ addresses and is the most common range for home networks.

IPv6 was designed to solve the address limitation problem of IPv4 as a major architectural priority.
IPv6 addresses are $128$ bits in length, significantly larger than the $32$ bits used in IPv4.
The total number of available IPv6 addresses is $340$ undecillion (calculated as $2^{128}$ ).
With a global population of approximately $6.8$ billion people, this provides a massive number of unique addresses per individual user, effectively removing all current and foreseeable address limitations.
IPv6 addresses are written in hexadecimal format rather than decimal to fit the large address into a manageable space.
Colons are used to separate the different sections (blocks) of the address instead of periods.
A full example of an IPv6 address is: $fe80:0000:0000:0000:5d18:0652:cffd:8f52$ .
Each block in the hexadecimal representation contains $16$ bits, meaning each block is equivalent to $2$ octets.
The entire address consists of $8$ blocks, totaling $128$ bits or $16$ bytes.

The complexity and length of IPv6 addresses make the Domain Name System (DNS) critical, as memorizing 128-bit addresses is difficult for humans. Fully-qualified domain names are used to reference these addresses.
Traditional subnetting is less common in IPv6 because the available address space is so vast.
In a standard IPv6 configuration, the address is split exactly in half:
- The first $64$ bits are the network prefix.
- The last $64$ bits are the host address (host ID).
The default subnet mask for most IPv6 implementations is a $/64$ .