The assignments must be made in accordance with the need presented by the ISP user and in accordance with existing recommendations [RIPE-690, https://www.ripe.net/publications/docs/ripe-690], of which the following stand out:

The end user or site must be assigned a prefix that is a multiple of “n” x /64, sufficient to meet their current and planned needs, and taking into account existing protocols and future possibilities, thus avoiding remuneration processes.

In IPv6 networks, it is allowed to assign at most one 64-bit network prefix for subnets due to several technical and design reasons that optimize the functionality and efficiency of the IPv6 protocol.

We detail the main reasons for this limitation:

1. Simplified autoconfiguration

IPv6 was designed to allow easier auto-configuration of devices on the network. With a 64-bit prefix, the last 64 bits of the IPv6 address can be used directly for interface address autoconfiguration (interface ID).

Devices can automatically configure their portion of the interface address using their MAC address (extended to 64 bits via the EUI-64 format) or by other unique interface ID generating mechanisms.

This division greatly simplifies the network configuration process, especially in home and business environments.

2. Optimization for local area networks

A 64-bit prefix is ​​ideal for most local area networks (LANs), as it provides enough unique addresses for any subnet imaginable. This avoids the need to renumber or change the addressing structure as devices are added to the network.

3. Support for ad hoc and mobile networks

IPv6 better supports ad hoc and mobile networks through the use of 64-bit prefixes, facilitating mechanisms such as configuring “on-the-fly” addresses for devices on mobile or temporary networks without the need for centralized network management.

4. Network standards and assured future

64-bit prefixes are standardized for most applications, ensuring compatibility and facilitating interoperability between different devices and manufacturers.

Maintaining a standard prefix size also helps future networking technologies and applications to develop on a consistent basis.

5. Support for Neighbor Discovery (ND) protocol

IPv6 uses the Neighbor Discovery protocol to detect and maintain information about neighboring devices. A 64-bit prefix optimizes this protocol, allowing efficient discovery and address table maintenance without requiring excessive use of network resources.

In summary, limiting prefixes to 64 bits in IPv6 is designed to balance the need for sufficient unique addresses within a subnet and the ease of configuration and management, while maintaining the efficiency of network protocols and facilitates future network expansion.