VLANs usually don’t extend past the WAN however there are new alternatives that exist today that allow VLAN traffic to pass through a WAN.
- 802.1ad Provider Bridges
- 802.1ah Provider Backbone Bridges
- Layer 2 Tunneling Protocol (L2TPv3)
- Ethernet over MPLS (EoMPLS)
- VLAN Private LAN Services (VPLS)
802.1Q-in-Q allows a Service Provider to preserve 802.1Q VLAN tags across a WAN service. Doing so allows a VLAN to span multiple geographically dispersed sites.
The ingress SP switch takes the 802.1Q frame and then adds an additional tag with another 802.1Q header defining the SP VLAN that ‘tunnels’ the customer VLAN across the WAN.
S-tag = Service provider imposed 802.1Q header
C-tag = Customer provided 802.1Q header