L3 VPN is an IP/MPLS Layer 3 VPN Service. So, it uses the same Labels used in IP/MPLS. In MPLS and VPLS articles we have talked about MPLS Labels. Here, we will explain these Labels again for VPRN Service too.
Basically, L3 VPN uses two MPLS labels. These MPLS labels are:
• Outer Label (Transport, LSP Label)
• Inner Label (Service, VPN Label)
Outher Label is the Transport/LSP Label. Swap process is done with this label in the Service Provider Network. In each hop, it is changed.This label is used for used in end-to-end LSPs. So it is also called LSP Labels. And used between PE devices.
Inner Label is the Service/VPN Label. In Service Provider Network it remains unchanged. It is used by PE routers to determine the L3 VPN service. The other name of this label is VPN Label. It identifies the specific customers and determine the destination of L3 VPN Service.
These Labels are assigned at the PE Router. And in the Service Provider Core, only Outher Label is swapped. At the PEs, according to Service Labels, L3 VPN Service is determined.
Do not worry about the names of the labels. To sum up there is only two Labels (can be named differently). One is used between PE devices for transport only, the other is transfered between PEs, but used only on PE devices to determine the L3 VPN Service.
In the Control and Data Plane Activities, we will talk about these Labels more detailly.You will also see the travel of Labels through the Service Provider Network. You will see, the Labelling steps from Label assigning to the label remove.
To learn more about L3 VPN, go through the other L3 VPN articles.