Table of Contents
IPv6 address types
There are three types of IPv4 addresses, unicast, multicast, and broadcast. In IPv6, broadcast addresses have been eliminated and replace with anycast and multicast addresses.
The IPv6 addresses Examples
Do you know what is IPv6 Address? What is your IPv6 Address? You can check your IPv6 address by typing the command “ipconfig” in the command prompt.
Unicast: represents a single interface. Packets addressed to a unicast address are delivered to a single interface.
Multicast: represents a dynamic group of hosts. Multicast addresses in IPv6 have a similar purpose as their counterparts in IPv4 and packets sent to these addresses are delivered to all interfaces turned into the multicast address.
Anycast: identifies one or more interfaces. For example, servers that support the same function can use the same unicast IP address. Packets sent to the IP address are forwarded to the nearest server. Anycast addresses are often used for load-balancing. Known as one-to-nearest address.
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There are three types of unicast addresses in IPv6.
Global unicast: publicly routable IPv6 addresses that work just like public IPv4 addresses.
IPv6 global unicast addresses are similar to IPv4 public addresses. A company that needs IPv6 addresses asks for a registered IPv6 address block, which is assigned as a global routing prefix. These addresses are routable on the Internet and only that company will use them.
Global unicast addresses start with 2000::/3 )hex 2 or 3).
They consist of two parts:
Subnet ID – 64 bits long. Contains the site prefix (obtained from a Regional Internet Registry0 and the subnet ID (subnets within the site).
Interface ID – 64 bits long. It acts like the IPv4 host field and is typically composed of a part of the MAC address of the interface.
Here is a graphical representation of the two parts of an IPv6 global unicast address:
| 3 bits | 45 bits | 16 bits | 64 bits |
| 0001 | Global Routing Prefix | Subnet ID | Interface ID |
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Link local: similar to the IPv4 addresses from the Automatic Private IP Address (APIPA0 range, these addresses are meant to be used only within a network segment that a host is connected to. Routers will not forward packets destined to a link-local address to other links. A link-local IPv6 address must be assigned to every network interface on which the IPv6 address must be assigned to every network interface on which the IPv6 protocol is enabled.
Here is the graphical representation of link local IPv6 address:
| 64 bits | 64 bits |
| FE80:0000:0000:0000 | Interface ID |
Unique local addresses: similar to IPv4 private addresses, IPV6 unique local addresses should be used inside an organization and are not meant to be routers on the Internet.
Unique local IPv6 addresses have the same function as private addresses in IPv4 – to allow communication throughout a site while being routable to multiple local networks. They are not registered with any numbering authority and cannot be routed to the internet. Unique local IPv6 addresses begin with FD00::/8.
A unique local IPv6 address is constructed by appending a randomly-generated 40-bit hexadecimal string to the FD00::/8 prefix. The subnet field and interface ID are created in the same way as with global unicast IPv6 addresses.
Here is a graphical representation of an unique local IPv6 address:
| 8 bits | 40 bits | 16 bits | 64 bits |
| FD | Global ID | Subnet ID | Interface ID |
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IPv6 EUI – 64 calculation
The second part of an IPV6 unicast address (used to identify a host’s network interface) is usually a 64-bit interface identifier. An interface ID is created by inserting the hex number FFFE in the middle of the MAC address of the network card. Also, the 7th bit in the first byte is flipped to a binary 1. The interface ID created this way is known as the modified extended unique identifier 64 (EUI – 64).
Here are the rules that a router uses to create the interface ID:
- Split the MAC address in two halves (6 hex digit each).
- Insert FFFE in between the two, making the interface ID.
- Invert the seventh bit of the interface ID.
For example, if the MAC address of a network card is 00:BB:CC:DD:11:22, the interface ID would be 02BBCCFFFFEDD1122.
Why is that so?
Well, the router will first flip the seventh bit from 0 to 1. MAC addresses are in hex format. The binary format of the MAC address looks like this:
Hex- 00BBCCDD1122
Binary – 0000 0000 1011 1011 1100 1100 1101 1101 0001 0001 0010 0010
The router will flip the seventh bit:
Binary – 0000 0000 1011 1011 1100 1100 1101 1101 0001 0001 0010 0010
This will result in the following hexadecimal address:
Hex – 02BBCCDD1122
Next, the router will insert FFFE in the middle of the address listed above:
Hex – 02BBCCFFFEDD1122
So, the interface ID will be 02BB:CCFF:FEDD:1122.
For interfaces that don’t have a MAC address (e.g. Serial interface), the router chooses the MAX of the lowest-numbered interface that has a MAC.
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