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Difficulty: EasyIPv6 Address Types and EUI-64

A network administrator configures a router interface using EUI-64 address generation with the command `ipv6 address 2001:db8:100:1::/64 eui-64`. If the physical MAC address of the interface is `bc24.1122.3344`, which 64-bit interface identifier will be automatically derived?

  1. BE24:11FF:FE22:3344Answer
  2. B
    BC24:11FF:FE22:3344
  3. C
    BE24:11FF:FF22:3344
  4. D
    BE24:1122:33FF:FE44

Answer

The derived interface identifier is BE24:11FF:FE22:3344.
The 64-bit EUI-64 interface identifier is generated by taking the 48-bit MAC address (`bc24.1122.3344`), inserting the 16-bit value `FFFE` in the middle (between `11` and `22`), and flipping the 7th bit of the first byte. The binary representation of `BC` is `10111100`; flipping the 7th bit yields `10111110`, which equals `BE` in hexadecimal format. Combining these results yields `BE24:11FF:FE22:3344`.

Step-by-Step Solution

1
Split the 48-bit MAC address into two 24-bit halves.
Left half: `BC-24-11`, Right half: `22-33-44`.
EUI-64 standard requires inserting a 16-bit value between the Organizationally Unique Identifier (OUI) and the NIC-specific portion.
2
Insert the 16-bit hexadecimal value FFFE into the midpoint.
`BC-24-11-FF-FE-22-33-44`.
Expands the 48-bit MAC address to a 64-bit structure.
3
Invert the 7th bit (Universal/Local bit) of the first byte.
First byte `BC` (binary `10111100`) becomes `BE` (binary `10111110`). Combining all parts in IPv6 format yields `BE24:11FF:FE22:3344`.
In EUI-64 addresses, setting the 7th bit to 1 specifies that the interface ID is globally unique.

Key Concept

EUI-64 Interface Identifier Generation
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Topics

IPv6 Address Types and EUI-64

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