The change in the CFI to DEI occurred between the 802.1q 2005 and the 2011 versions. In 802.1q 2005 section 9.6 Octet 1 bit 5 was defined for use as CFI (Canonical Format Indicator) whereas in the 2011 version of the standard (also shown in section 9.6), this bit has been redefined as the DEI (Discard Eligible Indicator) bit. The diagram is for a single .Q tag but I assume it also applies to additional tags. Cheers, Peter.
From: Nathan Ward [mailto:nznog(a)daork.net] Sent: Thursday, 9 October 2014 1:26 p.m. To: Brent Marquis; Dave Mill; Don Stokes Cc: nznog(a)list.waikato.ac.nz Subject: Re: [nznog] UFB Upload Issues
On 9 October 2014 at 1:09:42 pm, Brent Marquis (brent.marquis(a)chorus.co.nz(mailto:brent.marquis(a)chorus.co .nz))<mailto:brent.marquis(a)chorus.co.nz(mailto:brent.marqu is(a)chorus.co.nz))> wrote: >
Sorry for the quick reply to myself!
It actually seems like Don might not be 100% correct.
I don?t have IEEE access to get the .1q standard? But Wikipedia suggests it has been updated in 2005 for CFI to be DEI: > http://en.wikipedia.org/wiki/IEEE_802.1ad
Drop eligible indicator (DEI): a 1-bit field. (formerly CFI[note 1](http://en.wikipedia.org/wiki/IEEE_802.1Q#cite_note-2)[2 ](http://en.wikipedia.org/wiki/IEEE_802.1Q#cite_note-3)) May be used separately or in conjunction with PCP to indicate frames eligible to be dropped in the presence of congestion.[3](http://en.wikipedia.org/wiki/IEEE_802.1Q#ci te_note-4) > With the note suggesting ? ?IEEE 802.1Q-2005 clause 9.6?
If it?s on Wikipedia, it must be true?. Right? J
The quote above is from the 802.1q page. If you read the page you link to, the 802.1ad page, you get:
In IEEE 802.1ad the CFI is replaced by a Drop Eligibility Indicator (DEI), increasing the functionality of the PCP field.
Key bit is ?802.1ad?, not 802.1q. Using 0x88a8 vs 0x8100/0x9100 is signalling that you?re using 802.1ad vs. stacked 802.1q, so should set this bit appropriate to the tag type. I?m with Don on this one - the frame type bits signal how to interpret the following bits, you can?t just swap them around.
People should really just use 0x88a8 - those who aren?t, can I ask why not? Is it because you?re trying to tunnel it over a switch that doesn?t support 802.1ad or something? I?m not saying it?s wrong, I?m interested in understanding the situations in which you might do this.
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