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2.9.4. Modified EUI-64
A method to automatically generate the 64-bit interface ID from a device's MAC address:
- Split MAC (48 bits) into two halves
- Insert FFFE in the middle
- Flip the 7th bit (U/L bit)
Example:
MAC: 00:1A:2B:3C:4D:5E
Split: 00:1A:2B | 3C:4D:5E
Insert FFFE: 00:1A:2B:FF:FE:3C:4D:5E
Flip 7th bit: 02:1A:2B:FF:FE:3C:4D:5E
Interface ID: 021A:2BFF:FE3C:4D5E
The 64-bit interface ID is then appended to the 64-bit prefix (learned from a Router Advertisement under SLAAC, or given with ipv6 address 2001:DB8:1:1::/64 eui-64) to form the full 128-bit address.
⚠️ Exam Trap: EUI-64 creates predictable addresses from MAC addresses, which is a privacy concern. Privacy extensions (RFC 4941) generate random interface IDs instead.
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Written byAlvin Varughese
Founder•20 professional certifications