EUI-64 stands for Extended Unique Identifier.
EUI-64 is a method for creating a unique 64-bit interface identifier for IPv6 addresses. It is based on the 48-bit MAC address of the network interface, but with some modifications. The EUI-64 method is used to automatically configure IPv6 host addresses, without the need for manual configuration or DHCP.
An IPv6 device will use the prefix of its network and append its EUI-64 interface identifier to form a complete IPv6 address.
The main steps for generating an EUI-64 interface identifier are:
• Split the MAC address into two 24-bit parts: the Organizationally Unique Identifier (OUI) and the device identifier.
• Insert the hexadecimal value FFFE between the two parts, resulting in a 64-bit value.
• Invert the 7th bit of the first byte, which is called the universal/local (U/L) bit. This bit indicates whether the address is globally unique or locally administered.
For example, if the MAC address is 00-0C-29-2A-8C-A9, then the EUI-64 interface identifier would be: • Split the MAC address: 00-0C-29 | 2A-8C-A9 • Insert FFFE: 00-0C-29-FF-FE-2A-8C-A9 • Invert the 7th bit: 02-0C-29-FF-FE-2A-8C-A9
For example, if the network prefix is 2001:db8::/64, then the IPv6 address of the device with the EUI-64 interface identifier 02-0C-29-FF-FE-2A-8C-A9 would be:
2001:db8::020c:29ff:fe2a:8ca9
This address is also known as a stateless autoconfigured address or a link-local address.