In the IPv6 world, end-user devices use DHCP (Dynamic Host Configuration Protocol) or SLAAC (Stateless Address Auto Configuration) to dynamically learn IPv6 addresses, while routers use static IPv6 addresses. There is just one way to configuration static IPv4 addresses where the complete address is hard-coded in router configuration. IPv6 is a little different and there are actually two options to configure static IPv6 addresses on router interfaces.//
The first method that uses the ipv6 address command to define the entire 128-bit address has already been discussed in this chapter. The second method uses the same ipv6 address command to configure only the 64-bit IPv6 prefix for the interface letting the router automatically generate a unique interface ID. This second method uses a mechanism called EUI-64 (extended unique identifier). The configuration includes the eui-64 keyword to inform the router it has to use EUI-64 rules to create the interface ID portion of IPv6 address.////
Split the 12-hex-digit (6-byte/48-bit) MAC address into two halves of 6 hex digits each.
Insert hexadecimal FFFE in between the two halves making a total of 16 hex digits or 8 bytes/64 bits.
Invert seventh bit of the first byte in the 64-bit string, reading from left to right.
The following graphic elaborates these concepts for a router interface that has C200.1B2C.0000 as its MAC address.//
Figure 14-5 EUI-64 Interface ID Calculation