The interface identifier is a 64-bitdata field in the IPv6 address. It is used to identify nodes in subnets
.This identification is specified in the format by IEEE and is unique worldwide. The address format is the Extended Unique Identifier (EUI); it is an extended address format and uniquely identifies addresses of nodes and components globally. Since the EUI scheme comprises 64 bits, it is called EUI-64. Shorter network addresses occupy correspondingly less EUI-64 address space.