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Difficulty: MediumIPv6 Addressing and Prefixes

A network administrator enters the command `ipv6 address 2001:db8:1111:2222::/64 eui-64` on a Cisco router interface. If the MAC address of the interface is `1422.db88.99aa`, which IPv6 address will be automatically configured on the interface?

  1. 2001:db8:1111:2222:1622:dbff:fe88:99aaAnswer
  2. B
    2001:db8:1111:2222:1422:dbff:fe88:99aa
  3. C
    2001:db8:1111:2222:1622:db88:fffe:99aa
  4. D
    2001:db8:1111:2222:1622:dbff:fe88:99ab

Answer

The IPv6 address automatically configured on the interface is 2001:db8:1111:2222:1622:dbff:fe88:99aa.
The correct option demonstrates the precise three-step EUI-64 calculation process: splitting MAC address 1422.db88.99aa into two 24-bit halves, inserting FFFE in the center to form 64 bits, and flipping the seventh bit of the first byte (converting 0x14 to 0x16), resulting in 2001:db8:1111:2222:1622:dbff:fe88:99aa.

Step-by-Step Solution

1
Split the 48-bit MAC address into two 24-bit halves.
First half: 14-22-DB, Second half: 88-99-AA.
EUI-64 formatting requires inserting a 16-bit delimiter into the center of a standard 48-bit MAC address.
2
Insert the hex value FFFE between the two halves.
1422:DBFF:FE88:99AA.
FFFE is the standard 16-bit field inserted to expand a 48-bit MAC to a 64-bit interface identifier.
3
Invert the 7th bit (Universal/Local bit) of the first byte.
Hex 14 (binary 00010100) becomes Hex 16 (binary 00010110), yielding the interface ID 1622:dbff:fe88:99aa.
The IEEE EUI-64 standard flips the 7th bit of the OUI to represent universal scope when derived from a MAC address.
4
Combine the /64 IPv6 prefix with the calculated 64-bit interface ID.
2001:db8:1111:2222:1622:dbff:fe88:99aa.
The full 128-bit IPv6 address is constructed by appending the EUI-64 interface ID to the assigned prefix.

Key Concept

Modified EUI-64 Interface Identifier Generation
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Topics

IPv6 Addressing and Prefixes

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