What must you do with the first half of a MAC address when converting to EUI-64?

When converting a MAC address to EUI-64 format, the first half of the MAC address, which consists of the first three bytes (or 24 bits), is left unchanged when extending it to EUI-64. While combining the first half with the second half is crucial in the creation of a unique EUI-64 identifier, the actual operation involves an expansion that includes inserting the hex value FFFE in the middle of the MAC address rather than directly combining halves as the answer suggests. This process is meant to facilitate IPv6 address generation, where the full EUI-64 identifier consists of the original MAC address, extended by the insertion.

The EUI-64 format specifically adapts a 48-bit MAC address into a 64-bit format by inserting the additional FFFE between the two halves of the MAC address. Therefore, in the context of the answer, while the combining aspect is essential, it mainly emphasizes the use of the MAC address to create the full identifier, with the actual transformation occurring through the insertion of additional bits rather than a straightforward combination of two halves.