On 9/10/14 13:26, Nathan Ward wrote:
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.
For those playing along at home: - ethertype = 0x8100 means 802.1Q or 802.1aq or some pre-standard tag stacking - ethertype = 0x88a8 means 802.1ad (standardised double tagging) - ethertype = 0x9100, 0x9200, ... is pre-standard double tagging (looks like 0x9100 was the most common of those alternatives). See, eg, http://perlmonkey.blogspot.co.nz/2010/07/cisco-versus-ieee-qinq.html AFAICT the bit in that position in 802.1Q (0x8100) used to mean CFI (eg, 802.1Q-2003) and was changed by 802.1Q-2005 to mean DEI; the bit in that position in 802.1ad (0x88a8) seems to have always meant DEI. If the bit is clear (0), then the difference between 802.1Q-2003 and 802.1Q-2005 probably doesn't matter here; if it is set, it obviously does. Joy.
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.
Sadly it looks to be even less clear than that. Using 0x88a8 (as Nathan suggests) appears to clear up the confusion. But using 0x8100 appears to require asking "umm, which 802.1Q/802.1aq/pre-standard double-tagging thing was the sender following" if the CFI/DEI bit was set. So, eg, force clearing that bit as you receive it into your 0x8100 network (and, eg, apply your own QoS), upgrading everything to speak only modern 802.1Q (ie assume bit is always DEI), or using 0x88a8 (802.1ad) seem to be the only reasonably compatible options to avoid equipment confusion. Definitely looks like something that would benefit from being more clearly documented by Chorus as a technical item RSPs that choose 0x8100 as their ethertype and use this particular product should watch out for. Ewen PS: It appears one can get actual IEEE 802.1 standards as PDFs here: http://standards.ieee.org/about/get/802/802.1.html if one is willing to give up an email address to IEEE (I haven't actually tried to give them an email address though).