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Difficulty: MediumIPv6 Addressing and Prefixes

A network administrator is reviewing interface addressing rules and EUI-64 auto-configuration for an enterprise IPv6 rollout. Which two statements regarding IPv6 addressing characteristics and EUI-64 generation are correct? (Choose two.)

  1. The 7th bit of the MAC address's first octet (the Universal/Local bit) is inverted when constructing the 64-bit interface identifier.Answer
  2. The 16-bit hex value `FFFE` is inserted directly between the third and fourth octets (the middle) of the 48-bit MAC address.Answer
  3. C
    The 16-bit hex value `FFFE` is inserted between the first and second octets of the 48-bit MAC address to form the EUI-64 address.
  4. D
    An IPv6 `/64` subnet requires subtracting 2 host addresses from 2642^{64} because IPv6 maintains traditional IPv4 network ID and broadcast address reservations.

Answer

The two correct statements are: (1) The 7th bit of the MAC address's first octet (the Universal/Local bit) is inverted when constructing the 64-bit interface identifier, and (2) The 16-bit hex value `FFFE` is inserted directly between the third and fourth octets (the middle) of the 48-bit MAC address.
The EUI-64 process takes a 48-bit MAC address, splits it into two 24-bit sections, inserts `FFFE` in the middle between the third and fourth octets, and flips the 7th bit (Universal/Local bit) of the first byte. Thus, both statements describing these EUI-64 steps are correct.

Step-by-Step Solution

1
Analyze the EUI-64 expansion process for a 48-bit MAC address.
Confirm that the 48-bit MAC address is split into two 24-bit halves, inserting `FFFE` in the middle (between octet 3 and octet 4).
EUI-64 requires creating a 64-bit interface ID from a 48-bit MAC address by inserting `FFFE` into the center.
2
Analyze the bit inversion rule for EUI-64 generation.
Confirm that the 7th bit (Universal/Local bit) of the first byte of the MAC address is flipped from 0 to 1 (or 1 to 0).
RFC 4291 mandates modifying the 7th bit to reflect whether the address is globally unique.
3
Evaluate the IPv6 host reservation mechanics versus IPv4.
Recognize that IPv6 does not utilize broadcast addresses and does not subtract 2 addresses for broadcast and network IDs like IPv4.
Multicast replaces broadcast in IPv6, so standard IPv4 subnet host subtraction rules do not apply.

Key Concept

Modified EUI-64 Interface Identifier Generation and IPv6 Address Structure
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Topics

IPv6 Addressing and Prefixes

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