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Difficulty: Very hardIPv6 Addressing and Prefixes

A network engineer is configuring a Cisco router interface with a MAC address of `0050.568A.B1C2`. The interface is enabled for IPv6 using SLAAC with EUI-64 interface identifier generation under the prefix `2001:db8:1:1::/64`. Additionally, the engineer plans to configure a Unique Local Address (ULA) on the same interface. Which TWO statements regarding the IPv6 addressing for this interface are correct? (Select TWO.)

  1. The dynamically generated link-local IPv6 address on the interface is `fe80::250:56ff:fe8a:b1c2`.Answer
  2. Any valid Unique Local Address configured on this interface must fall within the prefix range `fc00::/7`.Answer
  3. C
    The automatically generated EUI-64 interface identifier derived from the MAC address is `0050:56ff:fe8a:b1c2`.
  4. D
    The `2001:db8:1:1::/64` subnet contains exactly 264−22^{64} - 2 usable host addresses because the all-zeros address is reserved for the subnet ID and the all-ones address is reserved for the IPv6 broadcast domain.

Answer

The correct statements are that the dynamically generated link-local IPv6 address is `fe80::250:56ff:fe8a:b1c2` and that any Unique Local Address must fall within the `fc00::/7` prefix block.
Generating an EUI-64 address from MAC `0050.568A.B1C2` involves inserting `FFFE` into the middle (`0050:56FF:FE8A:B1C2`) and toggling the 7th bit from 0 to 1 (`00` hex becomes `02` hex), producing interface ID `0250:56ff:fe8a:b1c2`. Prepended with `fe80::`, this forms the valid link-local address `fe80::250:56ff:fe8a:b1c2`. Furthermore, RFC 4193 specifies `fc00::/7` as the designated address range for IPv6 Unique Local Addresses.

Step-by-Step Solution

1
Calculate the EUI-64 interface identifier from MAC address `0050.568A.B1C2`.
Insert `FFFE` in the middle of the 48-bit MAC address: `0050:56FF:FE8A:B1C2`. Invert the 7th bit (Universal/Local bit) of the first byte: `00` (`0000 0000`) becomes `02` (`0000 0010`). The resulting EUI-64 interface ID is `0250:56ff:fe8a:b1c2`.
IEEE EUI-64 conversion rules mandate inserting `FFFE` between the OUI and NIC specific identifier and setting the 7th bit to 1 for globally unique MAC addresses.
2
Form the link-local address using the EUI-64 interface ID.
Combine `fe80::/10` with interface ID `0250:56ff:fe8a:b1c2` to get `fe80::250:56ff:fe8a:b1c2`.
Link-local addresses start with the `fe80::/10` prefix followed by 54 zero bits and the 64-bit interface identifier.
3
Identify the reserved prefix scope for IPv6 Unique Local Addresses (ULA).
ULAs are defined under `fc00::/7`.
RFC 4193 designates `fc00::/7` for Unique Local Unicast addresses, serving a role similar to RFC 1918 private IPv4 addresses.

Key Concept

EUI-64 Interface Identifier Generation & IPv6 Address Scopes
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Topics

IPv6 Addressing and Prefixes

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