MPLS mechanims uses two types MPLS Label to accomplish MPLS VPN Services. These are the two tunnel mechanims in MPLS mechnism. A Tunnel and many sub service tunnels in it.
Two types MPLS Labels that are used in MPLS VPN Services are :
• Transport Label (Outher Label)
• Service Label (Inner Label)
Transport Label is the Label that is swapped in the Service Provider MPLS network in each LSR. It is the main MPLS Label.
Service Label is the Label, that is used to determine MPLS VPN Services. They stay during swap process in MPLS network, they only tranport from one LER to another LER. At the ingress LER, it is pushed with Transport Label. At the Egress LER it is popped with the Trasnport Label.
It seems like a Six-shooter: )