Full form: Extended Unique Identifier 64-bit
Also known as: Extended Unique Identifier 64-bit
Quick Definition
A method of generating a 64-bit IPv6 interface ID from a 48-bit MAC address.
EUI-64 converts a device's 48-bit MAC address into a 64-bit interface ID for use in a SLAAC-generated IPv6 address. Process: split the MAC at the middle (after byte 3), insert FFFE in the middle, then flip the 7th bit (Universal/Local bit) of the first byte. Example: MAC 00:1A:2B:3C:4D:5E → EUI-64 host ID 021A:2BFF:FE3C:4D5E. The full IPv6 address prepends the /64 prefix from the RA.
MAC: 00:1A:2B:3C:4D:5E. Step 1: Split — 00:1A:2B | 3C:4D:5E. Step 2: Insert FFFE — 00:1A:2B:FF:FE:3C:4D:5E. Step 3: Flip 7th bit — 02:1A:2B:FF:FE:3C:4D:5E → 021A:2BFF:FE3C:4D5E.
The 7th bit flip is the hardest part of EUI-64 to remember. The CCNA exam may give you a MAC address and ask you to identify the correct EUI-64 interface ID. Practice converting binary 00 (0000 0000) → flip 7th bit → 02 (0000 0010).
A 48-bit hardware identifier burned into every network interface card.
A globally routable IPv6 address equivalent to a public IPv4 address (2000::/3).
An IPv6 mechanism where hosts automatically generate their own global address from the network prefix advertised by a router.
EUI-64 converts a device's 48-bit MAC address into a 64-bit interface ID for use in a SLAAC-generated IPv6 address. Process: split the MAC at the middle (after byte 3), insert FFFE in the middle, then flip the 7th bit (Universal/Local bit) of the first byte. Example: MAC 00:1A:2B:3C:4D:5E → EUI-64 host ID 021A:2BFF:FE3C:4D5E. The full IPv6 address prepends the /64 prefix from the RA.
The 7th bit flip is the hardest part of EUI-64 to remember. The CCNA exam may give you a MAC address and ask you to identify the correct EUI-64 interface ID. Practice converting binary 00 (0000 0000) → flip 7th bit → 02 (0000 0010).
MAC: 00:1A:2B:3C:4D:5E. Step 1: Split — 00:1A:2B | 3C:4D:5E. Step 2: Insert FFFE — 00:1A:2B:FF:FE:3C:4D:5E. Step 3: Flip 7th bit — 02:1A:2B:FF:FE:3C:4D:5E → 021A:2BFF:FE3C:4D5E.
EUI-64 falls under the IPv6 domain of the 200-301 exam. Understanding it in context with related terms like slaac and global-unicast-address is essential for answering scenario-based questions correctly.