Examkin

Question

Difficulty: MediumIPv6 Address Types and EUI-64

A network administrator executes the `show ipv6 interface gigabitethernet0/0/0` command on a Cisco IOS router. The interface has a burned-in MAC address of `3c4a.9211.2233` and is configured to generate its link-local address dynamically using the IEEE EUI-64 process. Which IPv6 link-local address will be assigned to this interface?

  1. fe80::3e4a:92ff:fe11:2233Answer
  2. B
    fe80::3c4a:92ff:fe11:2233
  3. C
    fe80::3e4a:92ff:ffff:2233
  4. D
    fc00::3e4a:92ff:fe11:2233

Answer

fe80::3e4a:92ff:fe11:2233
IPv6 link-local addresses use the FE80::/10 prefix. When generating a 64-bit interface identifier using EUI-64 from a 48-bit MAC address (3c4a.9211.2233), FFFE is inserted between the 3rd and 4th bytes (after 92), and the 7th bit (Universal/Local bit) of the first byte (0x3C = 0011 1100) is inverted to 1 (0x3E = 0011 1110). Combining FE80:: with 3e4a:92ff:fe11:2233 produces fe80::3e4a:92ff:fe11:2233.

Step-by-Step Solution

1
Identify the IPv6 address scope prefix required for interface link-local configuration.
Link-local addresses always begin with the prefix fe80::/10.
IPv6 interfaces automatically assign a link-local address in the fe80::/10 range when IPv6 is enabled.
2
Insert the 16-bit hex value FFFE into the middle of the 48-bit MAC address (3c4a.9211.2233).
Splitting 3c4a.92 and 11.2233 yields 3c4a:92ff:fe11:2233.
EUI-64 expands a 48-bit MAC address into a 64-bit interface identifier by inserting FFFE (1111 1111 1111 1110) in the middle.
3
Invert the 7th bit (Universal/Local bit) of the first byte of the MAC address.
First byte 0x3C in binary is 0011 1100. Inverting the 7th bit (from left) gives 0011 1110, which is 0x3E in hexadecimal.
IEEE EUI-64 rules dictate that the 7th bit of the first byte must be inverted (0 for globally unique/burned-in MACs becomes 1 to indicate local scope in the EUI-64 format).
4
Combine the link-local prefix with the resulting 64-bit EUI-64 interface identifier.
fe80::3e4a:92ff:fe11:2233
Concatenating the prefix fe80:: and the interface identifier 3e4a:92ff:fe11:2233 forms the final IPv6 link-local address.

Key Concept

EUI-64 Interface Identifier Derivation and Link-Local Address Formation
Rate this question

Topics

IPv6 Address Types and EUI-64

More questions from this topic