Examkin

Question

Difficulty: HardIPv6 Addressing and Prefixes

A network engineer is configuring a Cisco router interface with the command `ipv6 address 2001:db8:cafe:100::/64 eui-64`. The burn-in MAC address of the interface is `1866.DA12.3456`. Based on the IEEE EUI-64 process, which IPv6 global unicast address will be dynamically assigned to this interface?

  1. 2001:db8:cafe:100:1a66:daff:fe12:3456Answer
  2. B
    2001:db8:cafe:100:1866:daff:fe12:3456
  3. C
    2001:db8:cafe:100:1a66:dafe:ff12:3456
  4. D
    2001:db8:cafe:100:1a66:daff:fe12:3457

Answer

The dynamically generated IPv6 address assigned to the interface is 2001:db8:cafe:100:1a66:daff:fe12:3456.
The EUI-64 creation process takes the 48-bit MAC address (1866.DA12.3456), splits it into two 24-bit pieces, inserts FFFE in the middle (1866:DAFF:FE12:3456), and flips the 7th bit of the first byte (0x18 = 0001 1000 becomes 0x1A = 0001 1010). Appending this 64-bit interface ID to the specified 2001:db8:cafe:100::/64 prefix yields 2001:db8:cafe:100:1a66:daff:fe12:3456.

Step-by-Step Solution

1
Split MAC address into two equal 24-bit halves
Left half: 18-66-DA, Right half: 12-34-56
EUI-64 requires inserting a 16-bit hex value (FFFE) into the center of the 48-bit MAC address.
2
Insert FFFE between the two 24-bit halves
1866:DAFF:FE12:3456
This expands the 48-bit MAC address to a 64-bit interface identifier structure.
3
Invert the 7th bit (Universal/Local bit) of the first byte
First byte 0x18 (0001 1000 in binary) becomes 0x1A (0001 1010 in binary), making the interface ID 1a66:daff:fe12:3456
The IEEE EUI-64 standard specifies flipping the U/L bit (7th bit from left) to indicate whether the address is universally or locally administered.
4
Combine the /64 IPv6 prefix with the modified 64-bit interface ID
2001:db8:cafe:100:1a66:daff:fe12:3456
Concatenating the prefix 2001:db8:cafe:100::/64 with the EUI-64 interface ID creates the full 128-bit IPv6 global unicast address.

Key Concept

EUI-64 Interface Identifier Generation
Estimated Time:1m 30s
Rate this question

Topics

IPv6 Addressing and Prefixes

More questions from this topic