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.1q, .1qinq, .1ad, and TPIDs - General Discussion and Guidance


I work in a WAN environment and have an increasing need to understand the granular details of VLAN stacking. I've read  quite a bit in Cisco and other publications about .1q, the .1qinq extention, and the official IEEE .1ad protocols for frame tagging. My understanding is that .1ad is the formal adoption of .1qinq, but I don't know if there are any significant differences between the two other than the necessary configuration. I also understand that in both protocols, when configured, there can be as many as 3 vlan tags, 0,1, and 2, and the lowest number is considered the outer tag.

Where I get confused is the difference between and inner tag and outer tag, and the common reference to S-Tags and C-Tags. Can some one provide a comprehensive overview, or a link to such a resource, that covers TPIDs, the differences and presence of 0x8100 vs 0x9100 and other 0xXXXX TPIDs, and how they relate to service and customer tag names?

For instance, can a .1qinq frame contain two 0x8100 tags? Would these both be considered C-Tags? Are configuration mappings directed to the tag number or the TPID?

Also, in a WAN environment where as a service provider I am going to be introducing .1qinq or .1ad at my edge device, does my customer need to match that configuration, or can they operate transparently with standard .1q trunk/access ports?

Thank you for any references, clarification, and guidance you can provide.

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.1q, .1qinq, .1ad, and TPIDs - General Discussion and Guidance

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