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Zorluk: ZorIPv6 Address Types and EUI-64

A network engineer is inspecting an IPv6 neighbor discovery cache entry on a Cisco switch and identifies a connected host with the SLAAC-generated link-local address fe80::1e1b:0dff:fe44:5566fe80::1e1b:0dff:fe44:5566. Based on the EUI-64 address generation standard, what is the original burned-in MAC address of the host's network interface card?

  1. 1c1b.0d44.5566Cevap
  2. B
    1e1b.0d44.5566
  3. C
    1d1b.0d44.5566
  4. D
    1c1b.0dff.5566

Cevap

The original burned-in MAC address of the host is 1c1b.0d44.5566.
To reverse the EUI-64 process for the interface ID 1e1b:0dff:fe44:55661e1b:0dff:fe44:5566, first remove the 16-bit FFFEFFFE inserted in the middle to restore 48 bits: 1E−1B−0D−44−55−661E-1B-0D-44-55-66. Next, convert the first byte 1E1E to binary (0001 111020001\ 1110_2) and invert the 7th bit (counted from left to right), changing it from 1 to 0 to get 0001 110020001\ 1100_2 (1C1C). Reassembling the MAC address yields 1c1b.0d44.5566.

Adım Adım Çözüm

1
Identify the 64-bit interface identifier portion of the IPv6 link-local address.
The interface identifier is 1e1b:0dff:fe44:5566.
In a link-local address (fe80::/64fe80::/64), the last 64 bits represent the interface identifier.
2
Remove the 16-bit FFFEFFFE hexadecimal value inserted into the midpoint during EUI-64 derivation.
Removing FFFE from 1e1b:0dff:fe44:5566 yields the 48-bit pattern 1E-1B-0D-44-55-66.
EUI-64 generation inserts FFFEFFFE between the OUI (first 24 bits) and the vendor-assigned extension identifier (last 24 bits).
3
Invert the 7th bit (Universal/Local bit) of the first byte.
The first byte 1E1E (0001 111020001\ 1110_2) with its 7th bit inverted becomes 1C1C (0001 110020001\ 1100_2).
During EUI-64 formation, the 7th bit of the first MAC octet is inverted (0 for universal/burned-in becomes 1 for EUI-64). Reversing the process converts the 1 back to 0.
4
Reconstruct the 48-bit MAC address in standard Cisco dotted-quad hexadecimal notation.
Combining 1C−1B−0D−44−55−661C-1B-0D-44-55-66 into Cisco MAC format gives 1c1b.0d44.5566.
Cisco IOS formats MAC addresses as three groups of four hexadecimal digits separated by dots.

Anahtar Kavram

Reversing EUI-64 Interface Identifier Derivation to Extract Original MAC Address
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Konular

IPv6 Address Types and EUI-64

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