[STDS-802-11-TGAK] Proposal about 802.1Qbz
Let me raise a technical issue about 802.1Qbz on the mailing lists.
1. REMINDER OF CURRENT STATE
As we discussed in Geneva, P802.1Qbz D1.1 (and D1.2, now out for
balloting) uses a new way of stacking tags on LLC media. The result of
this method, applied consistently, is that everything in the frame is
length/type encoded except for the outermost tag or PDU, which is LLC
encoded. For example, an 802.11 IPgram with both a VLAN tag and a CN-tag
(never mind for a moment that we may not allow CN tags) would look like:
a: LLC-Ether encoding:
|AA AA 03 00 00 00 81 00|00 17|22 E9|12 34|08 00|ipheader ...
| LLC/SNAP |EthT |CVID |EthT |FloID|EthT | IPgram ...
This is different than the way that 802.1Q-2013, if applied as I read it,
says it would look like, which is:
b. LLC-Only encoding:
|AA AA 03 00 00 00 81 00|00 17|AA AA 03 00 00 00 22 E9|12 34|AA AA 03 00
00 00 08 00|ipheader ...
| LLC/SNAP |EthT |CVID | LLC/SNAP |EthT |FloID| LLC/SNAP
|EthT | IPgram Š
c. VLAN-tagged BPDU:
Just for contrast, an S-tagged 802.1D customer-tagged BPDU (which is
perfectly legal) encoded in LLC-Ether format would look like:
|AA AA 03 00 00 00 88 A8|00 48|00 26|42 42 03|BPDU Š
| LLC/SNAP |EthT |SVID |Lngth|D/SSAP C| protocol ID, Š
(The length field would not be present using the LLC-Only encoding)
d. Making a choice
In D1.1 and D1.2, the default operation is to use LLC-Ether encoding on
LLC media, and we have a variable that says, "Use LLC-Only encoding on
this port, instead of the default LLC-Ether encoding, if this is an LLC
medium. (We always use EtherType encoding on non-LLC media.)
2. THE QUESTION
Can we get rid of this variable, always do LLC-Ether encoding, and forget
about the LLC-Only encoding?
I'll follow up this question with my arguments in its favor, and invite
others to speak up on the issue, whether you agree with me or not. Feel
free, also, to ask questions about how and why we arrived at the point
where we are, now.
-- Norm
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