Network Engineering Stack Exchange is a question and answer site for network engineers. It only takes a minute to sign up.
Sign up to join this community
EUI-64 IPv6 addresses are generated from MAC addresses by taking the network prefix (64 bits) and appending the first half of the MAC address, then FF:FE, then the second half of the MAC. Is there a reason for the FF:FE? Other than 64+64=128.
Note: I didn't mention in the above that some bits in the prefix, specifically the "global" identifier and the "unique" identifier, get flipped.
0xFFFE was chosen by the IEEE as a reserved value to reflect the fact that a given address is in the modified EUI-64 format.
It's important to note that the first and second half of a MAC address actually have significance - the first being the organizationally unique identifier (OUI) that identifies the NIC manufacturer/class and the second being a number assigned by said manufacturer.
So - we have [8-byte prefix]+[3-byte OUI]+[FF-FE, 2 bytes]+[3-byte assigned NIC value] = 16 bytes, 128 bits.
Here is a good reference explaining the above.
