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“All Groups” multicast diagnostics request

“All Groups” multicast diagnostics request. Authors:. Date: 2008-08-07. Abstract. CID 301 in LB123 was resolved by adding a “magic” value of 7F-FF-FF-FF-FF-FE to indicate “any multicast frame”. However, this value is a legitimate multicast group address, so it needs to be changed.

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“All Groups” multicast diagnostics request

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  1. “All Groups” multicast diagnostics request Authors: Date: 2008-08-07 Alex Ashley, NDS Ltd

  2. Abstract CID 301 in LB123 was resolved by adding a “magic” value of 7F-FF-FF-FF-FF-FE to indicate “any multicast frame”. However, this value is a legitimate multicast group address, so it needs to be changed. Alex Ashley, NDS Ltd

  3. IEEE 802 MAC Address Format • [begin placing presentation body text here] Alex Ashley, NDS Ltd

  4. Hexadecimal Representation 3.1.8 hexadecimal representation: The representation of a sequence of octet values in which the values of the individual octets are displayed in order from left to right, with each octet value represented as a two-digit hexadecimal numeral, and with the resulting pairs of hexadecimal digits separated by hyphens. The order of the hexadecimal digits in each pair, and the mapping between the hexadecimal digits and the bits of the octet value, are derived by interpreting the bits of the octet value as a binary numeral using the normal mathematical rules for digit significance. Alex Ashley, NDS Ltd

  5. So 7F-FF-FF-FF-FF-FE is invalid because? • The LSB (bit 0) of octet zero is 1 • This means it is a group MAC address • Bit 1 of octet zero is 1 • This means that it is locally administered • So the address we chose could in theory be used as a valid group MAC address Alex Ashley, NDS Ltd

  6. Three Options • We need an address with the group bit reset, because this will never be confused with a multicast group • 7E-FF-FF-FF-FF-7E • Pro: A palindrome that is robust to bit ordering confusions • Con: A slightly more complex compare • 00-00-00-00-00-00 • Pro: A very simple compare • Con: OUI 000000 registered to Xerox • Any address with LSB bit zero • Pro: A simple compare • Con: No fixed value makes packet snoop debugging much harder Alex Ashley, NDS Ltd

  7. Straw Poll • Do you prefer option 1, 2 or 3 ? Alex Ashley, NDS Ltd

  8. Motion 1 • Move to instruct the TGv editor to replace the value “7F-FF-FF-FF-FF-FE” in sub-clause 7.3.2.21.10a of the TGv draft with “7E-FF-FF-FF-FF-7E” Alex Ashley, NDS Ltd

  9. Motion 2 • Move to instruct the TGv editor to replace the value “7F-FF-FF-FF-FF-FE” in sub-clause 7.3.2.21.10a of the TGv draft with “00-00-00-00-00-00” Alex Ashley, NDS Ltd

  10. Motion 3 • Move to instruct the TGv editor to replace: “The Group MAC Address field can be set to 7F-FF-FF-FF-FF-FE to indicate that all group addressed frames, apart from the broadcast MAC address, are requested.” in sub-clause 7.3.2.21.10a D3.0 of the TGv draft with: “A Group MAC Address field with the LSB of the first octet set to zero indicates that all group addressed frames, apart from the broadcast MAC address, are requested.” Alex Ashley, NDS Ltd

  11. References • IEEE Std 802-2001 - IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture Alex Ashley, NDS Ltd

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