CCIE: 802.1q (QinQ tunneling/802.1ad)
One of my personal favorite L2 subjects to discuss. When I was at the service provider this was a very cost effective Metro solution to extend customer VLANs. No routing protocols on the CPE and no expensive EoMPLS hardware required from the SP perspective. Simple and effective. You will hear many names for the outer tag (S-TAG, metro tag, etc…) just remember that the outer tag is the unique SP ID for that customer and the inner tags are the…