3.1.b Identify, implement and troubleshoot IPv6 addressing and subnetting

3.1.b [ii] EUI-64

Extended Unique Identifier (EUI) allows a host to assign itself a unique 64-bit IPv6 interface identifier (EUI-64). This feature is a key benefit over IPv4 as it eliminates the need of manual configuration or DHCP unlike IPv4. The IPv6 EUI-64 format address is obtained through the 48-bit MAC address. The Mac address is first separated into two 24-bits, with one being Organizationally Unique Identifier (OUI) and the other being NIC specific. The 16-bit 0xFFFE is then inserted between these two 24-bits to form the 64 -bit EUI address. IEEE has chosen FFFE as a reserved value which can only appear in EUI-64 generated from the an EUI-48 MAC address.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 2289-2292).  . Kindle Edition.

http://packetlife.net/blog/2008/aug/4/eui-64-ipv6/