Which Layer 3 VPN attribute causes customer routes to be installed into a VRF?

The Route Target (RT) attribute is crucial for Layer 3 VPNs because it dictates which routes are imported into and exported from a Virtual Routing and Forwarding (VRF) instance. When a Border Gateway Protocol (BGP) VPNv4 or VPNv6 route is received by a Provider Edge (PE) router, the router checks the RTs associated with that route against the import RTs configured for its VRFs. If there's a match, the route is installed into the corresponding VRF's routing table. The Route Distinguisher (RD) is used to make customer routes unique within the MPLS VPN backbone, preventing route overlap between different customers. It does not directly control route installation into a VRF. An extended community is a BGP attribute that carries additional information, and while RTs are a type of extended community, "extended-community" itself is too broad and doesn't specifically cause route installation. An MPLS label is used for forwarding traffic across the MPLS backbone, not for controlling route installation into a VRF.