In terms of IPv6, we have global unicast, unique local, and link-local addresses. Let's talk about global unicast today.
Global unicast addresses are similar to IPv4 public addresses. The addresses are assigned to individual hosts and have global reachability (unless they are blocked by security policies, such as firewalls). They are assigned from the range 2000::/3.Ever wonder how a host gets a unique global unicast address?Similar to IPv4 public IP addresses, IPv6 global unicast addresses are used when a host wants to access the internet.
There are three parts to a global unicast address
In the first 48 bits is known as the global routing prefix, in the next 16 bits is known as the subnet ID, and in the third part is known as the interface identifier or simply interface ID, which is part of the protocol that refers to the host.
2001:0d8:0000:0000:a111:b222:c333:abcd
👉 48 bit-- Global Routing Prefix
👉16- bit -- Subnet ID =65,535 possible subnets
👉64 bit--- Interface Identifier or Interface ID
In what way does your device receive a global unicast address?A two-step process are involved:
1️⃣ The 64-bit global routing prefix and subnet ID are part of the first part that comes from your default gateway.
2️⃣ A second 64-bit is generated by your device.
👉IANA (Internet Assigned Numbers Authority)
👉Your regional ISP
👉Your ISP
👉Your company's default gateway
The first 16 bits of an IPv6 global unicast address are usually assigned hierarchically. IANA, which manages DNS root, IP addressing, and other IP resources, sits at the very top, assigning the first 16 bits to anyone below.
For all global unicast addresses, 2001 is the first 16-bit number. If you see any IPV6 address that starts with 2001, you know it is a global unicast address.
In this example, your regional ISP will add 16 bits, such as DB8. As a result, anyone under your regional ISP would get 2001:DB8 as a routing prefix. In the third level, your ISP will add another 16-bit number, such as ABCD, so anyone downstairs will receive 2001:DB8:ABCD/48.
This is where the default gateway of your organization or company will add another 16 bit subnet ID such as 5678 as a routing prefix. As a result, any downstairs device will be assigned a 64-bit routing prefix.
It means if a company is assigned a /48 address by IANA which is common and uses /64 host address which is what they are supposed to do that leaves 16 bits for the company :)
My company is assigned 2001:DB8:ABCD::/48 by IANA, so it is able to assign subnets 2001:DB8:ABCD:0::/64 to 2001:DB8:ABCD:FFFF::/64 to its internal network segments.
Let's talk about the second 64-bit ID for your device. The second 64-bit portion, or interface ID, is derived from your device's mac address. As a result, the second portion is determined by your device, not by anyone else on the network.
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