EUI-64 Format Interface ID Creation from MAC Address

# How is an EUI-64 format interface ID created from a 48-bit MAC address?

### Question

How is an EUI-64 format interface ID created from a 48-bit MAC address?

### Explanations

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A. B. C. D. E.

D

An EUI-64 format interface ID is a 64-bit interface identifier that is used in IPv6 addressing. It is created by combining the 48-bit MAC address of a network interface card with a 16-bit number to form a unique 64-bit identifier. The process of creating an EUI-64 interface ID involves two steps: extending the 48-bit MAC address to 64 bits and modifying it to ensure its uniqueness.

The correct answer to this question is D. The process of creating an EUI-64 interface ID from a 48-bit MAC address involves inserting the value 0xFFFE between the upper three bytes and the lower three bytes of the MAC address. The resulting 64-bit number is the EUI-64 format interface ID.

Here is a step-by-step explanation of how this process works:

1. Take the 48-bit MAC address and split it into two 24-bit halves. For example, if the MAC address is 00:11:22:33:44:55, the two halves would be 001122 and 334455.

2. Insert the value 0xFFFE between the two halves. Using the example above, the result would be 001122FFFE334455.

3. Invert the seventh bit (the "u" bit) of the first half. The "u" bit is the second-to-last bit of the first byte of the MAC address. In our example, the seventh bit of the first half (001122) is the fifth bit of the second byte (11). Inverting this bit means changing it from a 1 to a 0 or vice versa. In our example, the result would be 001020FFFE334455.

4. The resulting number is the EUI-64 format interface ID. In our example, the EUI-64 format interface ID would be 001020FFFE334455.

The other answer options are incorrect:

A. by appending 0xFF to the MAC address. This is incorrect because appending 0xFF to the MAC address does not extend it to 64 bits or modify it to ensure its uniqueness.

B. by prefixing the MAC address with 0xFFEE. This is incorrect because prefixing the MAC address with 0xFFEE does not extend it to 64 bits or modify it to ensure its uniqueness.

C. by prefixing the MAC address with 0xFF and appending 0xFF to it. This is incorrect because this process results in a 56-bit identifier, not a 64-bit identifier.

E. by prefixing the MAC address with 0xF and inserting 0xF after each of its first three bytes. This is incorrect because this process results in a 60-bit identifier, not a 64-bit identifier, and it does not ensure uniqueness in the same way that the correct answer does.