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On 9 October 2014 at 1:09:42 pm, Brent Marquis (
brent.marquis@chorus.co.nz(mailto:
brent.marquis@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#cite_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.
--
Nathan Ward