Multiprotocol Label Switching (MPLS) Layer 3 VPNs are (predominantly) service-provider-provisioned VPNs that offer advantages such as any-to-any connectivity, support for real-time applications such as voice and video, and WAN routing simplicity for customers.
You can provision MPLS Layer 3 VPNs over an MPLS backbone network or an IP back-bone network (using GRE, L2TPv3, or other tunneling technologies). Unless otherwise specified, this chapter assumes that they are provisioned over an MPLS backbone.
MPLS Layer 3 VPNs are described in RFC 4364. They were formerly described in Internet Draft draft-ietf-l3vpn-rfc2547bis (RFC2547bis).
Figure 4-1 illustrates an MPLS backbone with two customer VPNs. ...