Oops, copy and passed the wrong link, but the right quote.



802.1Q  does show DEI, rather than CFI and appears to be a 2005 change to 802.1q standard.


Sorry for the confusion, but it would seem from the wiki information that Don would have been right if we were in 2004 (and/or possibly for anyone running software on switches from pre-2005 amendment to 802.1Q)







Brent Marquis | Layer 2 Network Specialist

 Chorus | T : +6448964169 | M :+64272290923


From: Nathan Ward [mailto:nznog@daork.net]
Sent: Thursday, 9 October 2014 1:26 p.m.
To: Brent Marquis; Dave Mill; Don Stokes
Cc: nznog@list.waikato.ac.nz
Subject: Re: [nznog] UFB Upload Issues



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

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