Examkin

Question

Difficulty: HardIPv6 Address Types and EUI-64

An administrator is inspecting SLAAC autoconfiguration logs on a host workstation connected to an enterprise switch port. The host has dynamically derived the link-local IPv6 address fe80::a8bb:ccff:fe11:2233fe80::a8bb:ccff:fe11:2233 using the standard IEEE EUI-64 process. Which 48-bit MAC address belongs to the physical network interface card of this host?

  1. aabb.cc11.2233Answer
  2. B
    a8bb.cc11.2233
  3. C
    a8bb.ccff.2233
  4. D
    acbb.cc11.2233

Answer

The physical MAC address of the host network interface is aabb.cc11.2233.
The MAC address aabb.cc11.2233 is correct because reversing the EUI-64 process involves removing the inserted midpoint sequence FFFE and toggling the 7th bit (Universal/Local bit) of the first byte. The first byte of the interface ID is hex A8 (binary 1010 1000). Toggling the 7th bit (the second least-significant bit of the byte) changes it to binary 1010 1010, which corresponds to hex AA. Combining AA with the remaining bytes after removing FFFE yields aabb.cc11.2233.

Step-by-Step Solution

1
Extract the 64-bit Interface Identifier from the link-local address.
Interface Identifier is a8bb:ccff:fe11:2233a8bb:ccff:fe11:2233.
The prefix fe80::/64fe80::/64 forms the network portion, while the last 64 bits represent the EUI-64 interface ID.
2
Remove the 16-bit ff:feff:fe sequence inserted into the midpoint of the EUI-64 address.
Splitting at ff:feff:fe yields a8:bb:cca8:bb:cc and 11:22:3311:22:33, forming a8bb.cc11.2233a8bb.cc11.2233.
During EUI-64 generation, 0xfffe0xfffe (1616 bits) is inserted between the OUI (first 24 bits) and the NIC-assigned portion (last 24 bits).
3
Invert the 7th bit (Universal/Local bit) of the first MAC octet.
First octet a8a8 (1010 100021010\ 1000_2) with 7th bit inverted becomes aaaa (1010 101021010\ 1010_2). Combining all octets gives aabb.cc11.2233aabb.cc11.2233.
EUI-64 creation toggles the 7th bit (U/L bit) of the first MAC byte. Reversing the operation requires toggling bit 7 back to its original state.

Key Concept

Deriving original MAC address from IPv6 EUI-64 interface identifier by removing FFFE midpoint insertion and toggling the Universal/Local (7th) bit.
Estimated Time:2m 0s
Rate this question

Topics

IPv6 Address Types and EUI-64

More questions from this topic