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Difficulty: HardIPv6 Addressing Concepts and Header Structure

A network administrator is deploying IPv6 using Stateless Address Autoconfiguration (SLAAC) on an enterprise network segment. A host interface on the segment has the MAC address `00:50:56:A1:B2:C3` and receives a Router Advertisement containing the prefix `2001:db8:cafe:10::/64`. Based on the Modified EUI-64 specification and RFC 5952 address compression rules, which of the following is the correct 128-bit IPv6 address configured by the host?

  1. 2001:db8:cafe:10:250:56ff:fea1:b2c3Answer
  2. B
    2001:db8:cafe:10:50:56ff:fea1:b2c3
  3. C
    2001:db8:cafe:10::250:56ff:fea1:b2c3
  4. D
    2001:db8:cafe:10:250:56fe:ffa1:b2c3

Answer

The correct IPv6 address is 2001:db8:cafe:10:250:56ff:fea1:b2c3.
The correct IPv6 address is constructed by splitting the 48-bit MAC address (00:50:56 and A1:B2:C3), inserting FFFE in between to form 0050:56FF:FEA1:B2C3, and inverting the 7th bit of the first byte (changing 00 to 02 to get 0250:56ff:fea1:b2c3). Applying RFC 5952 rules suppresses the leading zero in 0250 to 250. Concatenating the /64 prefix (2001:db8:cafe:10) with the interface ID yields 2001:db8:cafe:10:250:56ff:fea1:b2c3.

Step-by-Step Solution

1
Split the 48-bit MAC address into two 24-bit halves and insert FFFE in the middle.
MAC 00:50:56:A1:B2:C3 becomes 00:50:56:FF:FE:A1:B2:C3 (or 0050:56ff:fea1:b2c3 in 16-bit hextet notation).
Modified EUI-64 requires expanding a 48-bit MAC address to a 64-bit interface identifier by inserting the hexadecimal value FFFE into the middle.
2
Invert the 7th bit (Universal/Local bit) of the first byte.
The first byte 0x00 (binary 0000 0000) becomes 0x02 (binary 0000 0010), changing the first hextet from 0050 to 0250.
The IEEE EUI-64 format specifies that the 7th bit of the first byte indicates universal (0) or local (1) scope; inverting it designates a locally generated unique interface ID.
3
Apply RFC 5952 formatting rules for zero suppression.
The leading zero in hextet 0250 is suppressed to form 250, resulting in the 64-bit Interface Identifier 250:56ff:fea1:b2c3.
RFC 5952 mandates suppressing leading zeros within each 16-bit hextet.
4
Combine the /64 network prefix with the 64-bit Interface Identifier.
2001:db8:cafe:10:250:56ff:fea1:b2c3.
SLAAC appends the 64-bit EUI-64 Interface ID directly to the advertised 64-bit network prefix without inserting an extra double colon.

Key Concept

Modified EUI-64 Interface Identifier generation and RFC 5952 IPv6 address representation.
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Topics

IPv6 Addressing Concepts and Header Structure

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