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In a slideshow by IEEE regarding the Structured Local Address Plan (SLAP), I saw the following table:

SLAP local identifier SLAP Quadrant Z bit Y bit X bit M bit second hex digit
ELI 01 1 0 1 0 A
SAI 11 1 1 1 0 E
AAI 00 0 0 1 0 2
Reserved 10 0 1 1 0 6

This table shows that the M bit is zero; therefore the second hex digits are A, E, 2, 6. For example "1A-23-45-67-89-00" is an ELI.

I know that an ELI is a concatenation between a CID and a vendor-specific part. And IEEE states that in a CID, the M, X, Y, and Z bits have the values 0, 1, 0, and 1, respectively. So, this matches with the table.


However, in the standard IEEE 802c-Amd2, I saw the following table (The standard is not publicly available for free, but a screenshot of the table can be seen here):

Local MAC address type M bit X bit Y bit Z bit
ELI-48 I/G 1 0 1
ELI-64 I/G 1 0 1
SAI-48 I/G 1 1 1
SAI-64 I/G 1 1 1
AAI-48 I/G 1 0 0
AAI-64 I/G 1 0 0

This table shows that the M-bit is "I/G", so I interpret this notation that an ELI is an ELI based solely on its XYZ bits, independent of the M bit which can be 0 (I) or 1 (G).


My question is : What is "1B-23-45-67-89-00" ?

  • Is it a "Multicast ELI"? This would be weird because an ELI is based on a CID, and a CID is defined to have M-bit set to 0.

  • Is it a "Multicast EUI"? This would be weird because an EUI is based on a OUI, and a OUI is defined to have X bit set to 0.

  • Or is it neither an EUI or ELI, but something else?

The same question goes to:

  • "1F-23-45-67-89-00" ("Multicast SAI" or "Multicast EUI" or something else?)

  • "13-23-45-67-89-00" ("Multicast AAI" or "Multicast EUI" or something else?)

1 Answer 1

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Basically, the I/G bit (M here) isn't touched by that scheme, so yes, multicast is possible with SLAP. Note that Ethernet doesn't really distinguish between broadcast and multicast.

The standard doesn't claim that all possible combinations need to make sense.

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