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Difficulty: HardIPv6 Addressing and Prefixes

An engineer enters the following configuration command on a Cisco router interface whose hardware MAC address is `0A00.2712.3456`:

`R1(config-if)# ipv6 address 2001:db8:acad:b000::/64 eui-64`

Which fully compressed IPv6 global unicast address will be dynamically assigned to this interface?

  1. 2001:db8:acad:b000:800:27ff:fe12:3456Answer
  2. B
    2001:db8:acad:b000:a00:27ff:fe12:3456
  3. C
    2001:db8:acad::800:27ff:fe12:3456
  4. D
    2001:db8:acad:b000:800:27fe:ff12:3456

Answer

The correct dynamically generated address is 2001:db8:acad:b000:800:27ff:fe12:3456.
To derive the EUI-64 interface identifier from MAC address 0A00.2712.3456, insert FFFE between the 24-bit OUI and 24-bit NIC identifier to get 0A00:27FF:FE12:3456. Invert the 7th bit of the first hex byte (0A = 0000 1010 -> 08 = 0000 1000), resulting in 0800:27FF:FE12:3456. Combining this with prefix 2001:db8:acad:b000::/64 and suppressing the leading zero in 0800 yields 2001:db8:acad:b000:800:27ff:fe12:3456.

Step-by-Step Solution

1
Split MAC address and insert FFFE into the middle
MAC 0A00.2712.3456 becomes 0A00:27FF:FE12:3456.
EUI-64 generation requires expanding a 48-bit MAC address into a 64-bit interface ID by inserting FFFE (0xFFFE) between the OUI and device identifier.
2
Invert the 7th bit (Universal/Local bit) of the first byte
First byte 0A (binary 0000 1010) becomes 08 (binary 0000 1000).
The IEEE standard specifies that the 7th bit of the first byte must be inverted to indicate a globally unique, locally configured IPv6 interface identifier.
3
Combine the subnet prefix and interface ID, applying IPv6 compression rules
2001:db8:acad:b000:0800:27ff:fe12:3456 compresses to 2001:db8:acad:b000:800:27ff:fe12:3456.
Leading zeros within a hextet must be suppressed (0800 becomes 800), while non-zero fields like b000 retain their representation.

Key Concept

EUI-64 Interface Identifier Generation
Estimated Time:2m 0s
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Topics

IPv6 Addressing and Prefixes

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