In an MPLS VPN, how are customer routes controlled and distributed?

In MPLS VPNs, customer routes are controlled and distributed via route targets. Route targets are extended BGP communities that define which VPN routing and forwarding (VRF) instances can import or export specific routes. Each VRF has an import and an export route target list. When a route is exported from a VRF, it's tagged with the VRF's export route targets. Other VRFs that have matching import route targets can then import these routes, ensuring proper segregation and controlled distribution of customer traffic across the shared MPLS backbone. GRE tunnels are used for encapsulating traffic but don't inherently control route distribution in MPLS VPNs. Redistributing customer routes into the provider's IGP or provider BGP directly would merge customer routing information with the provider's core routing, leading to scalability issues, security risks, and loss of traffic separation.