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Difficulty: MediumIPv6 Address Types and EUI-64

A Cisco router interface GigabitEthernet0/1 has a burned-in MAC address of `0050.56a1.b2c3`. The interface is enabled and configured with the Cisco IOS command `ipv6 address fe80::/64 eui-64`. What is the complete compressed IPv6 link-local address assigned to this interface?

Answer: fe80::250:56ff:fea1:b2c3 / fe80::0250:56ff:fea1:b2c3 / FE80::250:56FF:FEA1:B2C3 / FE80::0250:56FF:FEA1:B2C3

Answer

fe80::250:56ff:fea1:b2c3
The standard EUI-64 process converts the 48-bit MAC address `0050.56a1.b2c3` by inserting `FFFE` into the midpoint (`0050.56FF.FEa1.b2c3`) and inverting the 7th bit of the first byte (`00` hex = `00000000` binary -> `00000010` binary = `02` hex). Appending this 64-bit interface identifier `0250:56ff:fea1:b2c3` to the link-local prefix `fe80::/64` yields `fe80::250:56ff:fea1:b2c3` after omitting leading zeros.

Step-by-Step Solution

1
Split the 48-bit MAC address into two 24-bit halves and insert the 16-bit hex value `FFFE` in the middle.
The MAC `0050.56a1.b2c3` becomes `0050:56FF:FEA1:B2C3`.
EUI-64 standard requires expanding a 48-bit MAC address into a 64-bit interface identifier by inserting `FFFE` between the OUI and the vendor-assigned NIC bytes.
2
Invert the 7th bit (Universal/Local bit) of the first byte.
First byte `00` (0000 000020000\ 0000_2) with the 7th bit inverted becomes `02` (0000 001020000\ 0010_2). The 64-bit Interface Identifier is `0250:56ff:fea1:b2c3`.
The 7th bit of the first byte indicates universal (00) vs local (11) scope; inverting 00 yields 11 (0202 hex).
3
Combine the link-local prefix `fe80::/64` with the generated EUI-64 interface identifier and apply standard IPv6 leading-zero compression.
`fe80::250:56ff:fea1:b2c3`
Link-local addresses always begin with `fe80::/64`, followed by the 64-bit interface identifier, suppressing leading zeros in hex quartets.

Key Concept

EUI-64 Link-Local IPv6 Address Calculation
Estimated Time:1m 30s
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Topics

IPv6 Address Types and EUI-64

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