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Difficulty: MediumIPv6 Addressing and Prefixes

A network administrator is configuring a router interface for IPv6 stateless address autoconfiguration (SLAAC) using EUI-64. The interface is assigned the IPv6 prefix 2001:db8:cafe:10::/642001:\text{db8}:\text{cafe}:10::/64 and has a MAC address of B4A9.5A12.3456\text{B4A9.5A12.3456}. Which complete IPv6 global unicast address will be generated for this interface?

  1. 2001:db8:cafe:10:b6a9:5aff:fe12:3456Answer
  2. B
    2001:db8:cafe:10:b4a9:5aff:fe12:3456
  3. C
    2001:db8:cafe:10:b6a9:5aff:ff12:3456
  4. D
    2001:db8:cafe:10:fffe:b6a9:5a12:3456

Answer

2001:db8:cafe:10:b6a9:5aff:fe12:3456
The address ending in 'b6a9:5aff:fe12:3456' is correct because EUI-64 splits the MAC address B4:A9:5A:12:34:56 into two equal parts, inserts the 16-bit hex value FFFE into the middle, and flips the 7th bit of the first byte (changing 0xB4, which is 1011 0100 binary, into 0xB6, which is 1011 0110 binary).

Step-by-Step Solution

1
Split the MAC address into two 24-bit halves and insert FFFE in the middle.
The MAC address B4:A9:5A : 12:34:56 becomes B4A9:5AFF:FE12:3456.
EUI-64 expands a 48-bit MAC address into a 64-bit interface identifier by inserting the 16-bit hex value FFFE between the OUI and the NIC specific serial number.
2
Invert the 7th bit (Universal/Local bit) of the first byte.
First byte 0xB4 in binary is 1011 0100. Inverting the 7th bit gives 1011 0110, which is 0xB6. The interface ID becomes b6a9:5aff:fe12:3456.
RFC 4291 requires flipping the 7th bit of the first byte to indicate universal scope for IEEE MAC-derived interface identifiers.
3
Combine the /64 network prefix with the generated 64-bit interface identifier.
2001:db8:cafe:10:b6a9:5aff:fe12:3456.
The full IPv6 address is constructed by appending the EUI-64 interface ID to the assigned /64 network subnet prefix.

Key Concept

EUI-64 Interface Identifier Generation
Estimated Time:1m 15s
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Topics

IPv6 Addressing and Prefixes

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