IPv6

Why IPv6?

The Internet Engineering Task Force (IETF) created IPv4 (RFC 791) with an address space of 4.3 billion, initially believed to be sufficient for all devices connecting to the Internet. However, as early as the late 1980s, when the Internet began to flourish, experts foresaw the eventual exhaustion of IPv4 addresses.

What is IPv6?

IPv6 is newer and better version of Internet Protocol bringing about 3.4*10^38 total addresses and many provides other technical benefits such as hierarchical address allocation methods & multicast addressing is expanded and simplified. Do note that IPv4 and IPv6 are not interoperable.

The IPv6 Address

Remember IPv4 address looks like this:

The bits refer to the binary digits of the address.

$$ \underbrace{192.168.32.152}_{\text{32-bit in length}} $$

is made up four sections called octets, each octet can contain any number between 0-255:

$$ \underbrace{192}_{\text{octet}}.\underbrace{168}_{\text{octet}}.\underbrace{32}_{\text{octet}}.\underbrace{152}_{\text{octet}} $$

Let's look at IPv6 address:

$$ \text{2001:0db8:0000:0000:a111:b222:c333:abcd} $$

Things to note with IPv6:

In comparison to IPv4 which is 32 bits long, IPv6 address is 128 bits long.
IPv4 has 4 sections calles octets, but IPv6 has 8 sections called hextets.
IPv4 uses . to separate octets. IPv6 uses : to separate hextets.

IPv6 in Binary

IPv4 is usually represented in decimal format, but IPv6 is hexadecimal that is it is generally represented using any character between 0-9 and a-f.

Each hexadecimal character is made up of four binary bits which can be 0 or 1. Each bit represents a value of 1, 2, 4 or 8. It doubles with each column from right to left.

$$ \def\arraystretch{1.5} \begin{array}{c:c:c:c} 8 & 4 & 2 & 1 \\ \hline 0 & 0 & 0 & 0 \\ \end{array} $$

Wherever we see a 1, that toggles that column on, and wherever we see a 0 that toggles that column off.

We then add up all of the columns that have a 1 and this gives us our number or letter.

To make the number 2 from our binary bits, we switch on the column for 2. Giving us the binary value for our first number: 0010.
To make the second number 0 from our binary bits, we keep all bits off.

$$ \underbrace{ \textcolor{#07fc03}{2} }_{\text{0010}} \text{001:0db8:0000:0000:a111:b222:c333:abcd} \newline \def\arraystretch{1.5} \begin{array}{c:c:c:c} 8 & 4 & 2 & 1 \\ \hline 0 & 0 & \textcolor{#f56c42}{1} & 0 \\ \end{array} $$

$$ \text{2} \underbrace{ \textcolor{#07fc03}{0} }_{\text{0000}} \text{01:0db8:0000:0000:a111:b222:c333:abcd} \newline \def\arraystretch{1.5} \begin{array}{c:c:c:c} 8 & 4 & 2 & 1 \\ \hline 0 & 0 & 0 & 0 \\ \end{array} $$

For d (or any alphabet), it gets interesting. The hexadecimal digits ends at f like this:

$$ \def\arraystretch{1.5} \begin{array}{} 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & a & b & c & d & e & f \\ 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & 11 & 12 & 13 & 14 & 15 \\ \end{array} $$

We should always start with the highest number you can in our original table in order to achieve our desired digit and in this case that number is 8.

So, to achieve 13 or d, we'll try representing 13 in binary like this:

$$ \text{2001:0000:0} \underbrace{ \textcolor{#07fc03}{d} }_{\text{1101}} \text{b8:0000:0000:a111:b222:c333:abcd} \newline \def\arraystretch{1.5} \begin{array}{c:c:c:c} 8 & 4 & 2 & 1 \\ \hline 1 & 1 & 0 & 1 \\ \end{array} $$

Continuing this we'll achieve this binary digits:

$$ 10000000000001:110110111000:000000000000:000000000000:1010000100010001:1011001000100010:1100001100110011:1010101111001101 $$

Network Section

Just like IPv4, IPv6 has network section.

$$ \underbrace{\textcolor{#ecf549}{2001}:\textcolor{#ecf549}{0db8}:\textcolor{#ecf549}{0000}:\textcolor{#ecf549}{0000}}_\text{Network section}: \underbrace{a111:b222:c333:abcd}_\text{Host section}\textcolor{#ecf549}{/64} $$

IPv4 uses subnet mask to define this network section, however IPv6 gets rid of subnet mask and instead it just uses a / and number of network bits.

In above example $\textcolor{#ecf549}{64}$ is half of our 128 bit address. /64 addresses are common when it comes to IPv6.

Compressing the Address

The first trick is to remove continuous zeroes and replace it with double colon, computer can then figure out there are two missing hextets and then it fill it up with zeroes.
- The rule to this is it can only appear once.
$$ \text{2001:0db8:\underline{0000:0000}:a111:b222:c333:abcd} \newline \text{2001:0db8\textcolor{#ecf549}{::}a111:b222:c333:abcd} $$

So, this we cannot do!

$$ \text{2001:0db8:\underline{0000:0000}:a111:b222:0000:abcd} \newline \text{2001:0db8\textcolor{#ecf549}{::}a111:b222\textcolor{#ecf549}{::}abcd} $$
Second trick, we can all leading zeroes from each hextets and remove them:

$$ \text{2001:\textcolor{#ecf549}{0}db8\textcolor{#ecf549}{::}a111:b222:\textcolor{#ecf549}{000}0:abcd} \newline \text{2001:db8\textcolor{#ecf549}{::}a111:b222:0:abcd} $$
- We need to leave last 0 is second last hextet since we already placed ::.

Global Unicast address

Just like IPv4 there are different type of IPv6 addresses and they serve different purposes.

This one is Global unicast address, unlike IPv4, we don't need to rely on private addresses. Every device can have it's own public IP addresses.

$$ \underbrace{ \textcolor{#ecf549}{2001:0db8:0000} }_{\text{Global Prefix}} \text{:0000:a111:b222:c333:abcd} $$

The first part of IPv6 Global prefix is called atleast 48 bits long Global Prefix which is provided by your ISP (Internet service provider).

After Global prefix, we use the next 16-bits for subnet IDs.

16 bits give us over 65,000 subnets to play with

$$ \underbrace{ \textcolor{#ecf549}{2001:0db8:0000} }_{\text{Global Prefix}}: \overbrace{ \textcolor{#07fc03}{0000} }^{\text{Subnet ID}} \text{:a111:b222:c333:abcd} $$

The remaining 48-bits can then be used for host or interface ID

$$ \underbrace{ \textcolor{#ecf549}{2001:0db8:0000} }_{\text{Global Prefix}}: \overbrace{ \textcolor{#07fc03}{0000} }^{\text{Subnet ID}}: \underbrace{ \text{a111:b222:c333:abcd} }_{\text{Interface ID}}: $$

Other address type

Address type
Global unicast	`2000::/3`	Publicly routable
Unique local	`fc00::/7`	Routable in the LAN
Link local	`fe80::/10`	Not routable
Multicast	`ff00::/8`	Addresses for groups
Anycast	`2000::/3`	Shared address

Global Unicast (2000::/3): The prefix to identify these address is like 2000::/3 which means, the /3 first three bits identify a global unicast address are fixed. It will start with either a 2 or a 3
- i.e. the address will lie in range 2000::/3 to 3fff::/3. And in binary notation, the first 3 bits will remain contant
- addresses in 2000:: to 3fff:ffff:fff1f:ffff:ffff:ffff:ffff:ffff
- So in binary addresses starting with
  
  $$ \textcolor{#07fc03}{0010}{000000000000}:0000000000000000:0000000000000000:0000000000000000:0000000000000000:0000000000000000:0000000000000000:0000000000000000 $$
  
  to address:
  
  $$ \textcolor{#07fc03}{0011}{111111111111}:1111111111111111:1111111111111111:1111111111111111:1111111111111111:1111111111111111:1111111111111111:1111111111111111 $$
- Globally unique and routable, similar to public IPv4 address.
Unique local (fc00::/7): These are like IPv4 private address, not gloabally routable but routable only within the scope of private networks.
- Unique local address will always start with f followed by either c or a d
- Unique local addresses may be used freely, without centralized registration, inside a signle site or organization.
Link local (fe80::/10): Link-local addresses allow communication between neighboring nodes without needing a globally unique address. IPv6 routers do not forward data with link-local addresses beyond the local network. All IPv6-enabled interfaces automatically have a link-local unicast address.
Think of this as similar to 169.254.xxx.xxx of IPv4.
Are crucial for tasks like automatic address configuration and for the Neighbor Discovery Protocl (NDP), which help devices on the same link find and communicate with each other.
Mulicast (ff00::/8): These addresses are sent to a group of nodes listening for that particular multicast address.
IPv6 abolishes IPv4 broadcast communication completely, replacing it with IPv6 multicast, implemented using Protocol Independent Multicast (PIM) routing.
Anycast (2000::/3): IPv6 allows us to assign the same IP address to multiple devices. The data is then sent to the closest device with that address. There isn't a specific range for anycast address, they use the same address space as global unicast address.