In the context of IPv6, concerns about duplicate IP addresses are handled significantly differently compared to IPv4, thanks to the vast number of addresses available and specific mechanisms designed to prevent address collisions.

IPv6 Address Space

IPv6 uses 128-bit addresses, providing approximately 340 undecillions (3.4 × 10^38) unique addresses, thus offering virtually unlimited address space to assign unique addresses to every device on the Internet without risk of exhaustion or need for intensive reuse. as in IPv4.

Address Assignment Mechanisms

To handle the issue of duplicate addresses in IPv6 networks, several mechanisms are used:

1. Stateless Address Autoconfiguration (SLAAC): This method allows devices on an IPv6 network to automatically configure their own IP address using the device's MAC address as part of the IPv6 address, reducing the possibility of duplicates. Still, a check is performed to ensure that the generated address is unique on the local network.
2. Duplicate Address Detection (DAD): Before an IPv6 address is definitively assigned to a device, a process known as Duplicate Address Detection is performed. The device sends a Neighbor Solicitation packet on the network to check if any other interface is already using the proposed address. If the address is discovered to be in use, the autoconfiguration process stops using that address and attempts to generate another one.
3. Dynamic Host Configuration Protocol for IPv6 (DHCPv6): Like its IPv4 counterpart, DHCPv6 can assign IP addresses to devices on a network. DHCPv6 has its own mechanisms to prevent the assignment of duplicate addresses by keeping a record of all the addresses it has assigned.

Address Management in Practice

In practice, the combination of an almost unlimited address space with robust automatic mechanisms and duplicate detection makes the possibility of facing a duplicate IP address in IPv6 extremely low.

However, in the unlikely event of an address collision, built-in mechanisms like DAD are designed to resolve the issue automatically by prompting the device to select a new address.

Security Considerations

Although the automatic handling and vast number of addresses in IPv6 reduce the risk of duplicate addresses, it also poses unique security challenges, such as tracking devices through their IPv6 addresses.

Therefore, IPv6 introduces concepts such as “Privacy Extensions” addresses, which periodically change the part of the address that could be used to identify a device, helping to protect user privacy.

In summary, IPv6 is designed with mechanisms that effectively handle the problem of duplicate IP addresses, making this problem much less common and concerning compared to IPv4.