1. “All Groups” multicast diagnostics request
September 2008
doc.: IEEE /0963r2
September 2008
“All Groups” multicast diagnostics request
Date:
Authors:
Alex Ashley, NDS Ltd
Alex Ashley, NDS Ltd

2. September 2008
doc.: IEEE /0963r2
September 2008
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.
301
There is no ability to make a wildcard multicast MAC address request - "i..e report on all multicast groups you participate in" [This is a "lost" D1.0 comment]
Alex Ashley, NDS Ltd
Alex Ashley, NDS Ltd

3. IEEE 802 MAC Address Format
September 2008
IEEE 802 MAC Address Format
[begin placing presentation body text here]
Alex Ashley, NDS Ltd

4. Hexadecimal Representation
September 2008
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?
September 2008
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. September 2008
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
Pro: A very simple compare
Con: OUI 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 ? September 2008
Alex Ashley, NDS Ltd

8. September 2008
Motion 1
Move to instruct the TGv editor to replace the value “7F-FF-FF-FF-FF-FE” in sub-clause a of the TGv draft with “7E-FF-FF-FF-FF-7E”
Alex Ashley, NDS Ltd

9. September 2008
Motion 2
Move to instruct the TGv editor to replace the value “7F-FF-FF-FF-FF-FE” in sub-clause a of the TGv draft with “ ”
Alex Ashley, NDS Ltd

10. Motion 3 Move to instruct the TGv editor to replace:
September 2008
doc.: IEEE /0963r2
September 2008
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 a 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
Alex Ashley, NDS Ltd

11. September 2008
References
IEEE Std IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture
Alex Ashley, NDS Ltd