Unique Local Address

Unique local IPv6 unicast addresses, also known as Unique Local Addresses (ULAs), are a type of IPv6 address used for communication within a specific local network.

Unlike global addresses, which are routable over the Internet, ULA addresses are designed to be used on private networks and do not propagate beyond them. Below is a detailed explanation of unique local unicast IPv6 addresses:

ULA address range:

ULA addresses are defined in the address range “fc00::/7”. This range is divided into two parts:

• First 8 bits: The “fc00::/8” prefix is ​​reserved for organization-defined or locally significant addresses.
• Next 40 bits: The next 40 bits are randomly generated or derived from the MAC address of the network interface to create a unique identifier within the local network.

Scope and routing:

ULA addresses have a limited scope to the local network or the set of interconnected private networks. These addresses are not routed over the public Internet and are therefore not accessible from outside the local network.

Purpose and use:

ULA addresses are used for internal communication within an organization or private network. These addresses provide a consistent and unique form of addressing within the network, regardless of changes in Internet Service Providers (ISPs) or assigned global IPv6 addresses.

ULA address generation:

ULA addresses can be generated in different ways:

• Manually: Organizations can manually select and assign a range of ULA addresses for internal use.
• randomly: ULA addresses can be generated randomly using an algorithm or random number generator.
• Derived from the MAC address: It is also possible to derive part of the ULA address from the MAC address of the network interface, ensuring uniqueness within the local network.

Interoperability with global addresses:

ULA addresses can be used in conjunction with global IPv6 addresses on a network. This allows devices to communicate using ULA addresses within the local network and use global addresses for communication outside the local network.

Internal routing considerations:

Although ULA addresses are not routed over the public Internet, it is important to configure proper internal routing within the local network to ensure connectivity and communication between devices using ULA addresses.

Privacy & Security:

ULA addresses provide an additional level of privacy and security compared to global IPv6 addresses. Because ULA addresses are not routed over the public Internet, they are not visible or accessible from outside the local network. This helps protect the network from potential external threats and reduces devices' exposure to malicious attacks.

Coexistence with global addresses:

In a network that uses ULA addresses and global addresses, it is important to ensure coexistence and communication between devices that use both types of addresses. This can be achieved by using address translation techniques (such as NAT64) or by proper routing between ULA addresses and global addresses.

Name resolution:

To facilitate communication using ULA addresses, it is recommended that you configure an internal name resolution system on the network. This allows you to assign meaningful names to ULA addresses and simplify access to devices within the local network.

Documentation and registration:

It is important to document and record the ULA addresses used on a local network to keep track of assignments and avoid address conflicts. This helps efficiently manage addressing and facilitates long-term network administration.

In conclusion

IPv6 unique local unicast addresses (ULAs) are used for internal communication on a local network or set of private networks. They provide a unique and secure addressing scheme within the network, with a limited reach to the local network. ULA addresses offer privacy and allow coexistence with global IPv6 addresses, improving the security and efficiency of the local network.