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Difficulty: HardIPv6 Address Types and EUI-64

A network administrator is verifying IPv6 autoconfiguration on a Cisco router interface. The interface has a burned-in MAC address of `7069.5a12.3456` and is configured with the command `ipv6 address 2001:db8:abc:10::/64 eui-64`. Based on standard EUI-64 interface identifier construction and IPv6 address formats, which TWO statements regarding the resulting IPv6 configuration on this interface are correct?

  1. The derived 64-bit EUI-64 interface identifier for this interface is `7269:5aff:fe12:3456`.Answer
  2. The dynamically generated link-local IPv6 address for this interface begins with the `fe80::/10` prefix combined with the modified interface identifier.Answer
  3. C
    The EUI-64 calculation inserts the 16-bit hexadecimal sequence `ffff` into the midpoint of the 48-bit MAC address.
  4. D
    The 7th bit (universal/local bit) of the MAC address is left un-inverted, yielding an interface identifier beginning with `7069`.
  5. E
    Executing the command with the `eui-64` keyword automatically creates a link-local address within the unique local address scope (`fc00::/7`).

Answer

The two correct statements are: (1) The derived 64-bit EUI-64 interface identifier for this interface is `7269:5aff:fe12:3456`, and (2) The dynamically generated link-local IPv6 address for this interface begins with the `fe80::/10` prefix combined with the modified interface identifier.
Generating an IPv6 EUI-64 interface identifier from a 48-bit MAC address requires two transformations: toggling the 7th bit of the first byte (changing 0x70 to 0x72) and inserting FFFE into the midpoint, forming the 64-bit identifier `7269:5aff:fe12:3456`. Additionally, IPv6 automatically configures a link-local address on the interface using the designated prefix `fe80::/10` combined with this EUI-64 identifier.

Step-by-Step Solution

1
Split the 48-bit MAC address into two 24-bit halves
Left half: `70-69-5A`, Right half: `12-34-56`
EUI-64 generation requires inserting a 16-bit delimiter into the middle of the MAC address.
2
Invert the 7th bit (Universal/Local bit) of the first byte
First byte `0x70` in binary is `0111 0000`. Inverting the 7th bit (2nd least significant bit of first byte) yields `0111 0010` in binary, which is `0x72`. The first half becomes `7269.5a`.
Inverting the U/L bit indicates that the address has been modified for global uniqueness scoping in IPv6 EUI-64.
3
Insert `FFFE` at the midpoint between the two halves
`7269:5A` + `FFFE` + `:123456` = `7269:5aff:fe12:3456`
This expands the 48-bit MAC address into a 64-bit interface identifier.
4
Verify the link-local prefix and global unicast address formation
Link-local address = `fe80::7269:5aff:fe12:3456`, Global unicast address = `2001:db8:abc:10:7269:5aff:fe12:3456`
Link-local addresses always use the `fe80::/10` prefix block (specifically formatted as `fe80::/64`).

Key Concept

IPv6 EUI-64 Interface Identifier Derivation and Link-Local Address Scoping
Estimated Time:2m 0s
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Topics

IPv6 Address Types and EUI-64

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