How are local CE routes associated with the appropriate VRF at the PE?

In a Virtual Private Routed Network (VPRN), a Provider Edge (PE) router maintains multiple independent routing tables, one for each VPN, known as a Virtual Routing and Forwarding (VRF) instance. The association of incoming routes from a Customer Edge (CE) device to the correct VRF is determined by the specific physical or logical interface on the PE router that receives the routing update. Each customer-facing interface on the PE is explicitly bound to a single VPRN service (and its corresponding VRF). Therefore, all routes learned via a particular interface are automatically placed into the routing table of the VRF associated with that interface.

B. Based on the Route Distinguisher.

The Route Distinguisher (RD) is prepended to an IPv4 prefix to create a unique VPN-IPv4 prefix. This happens after the route is placed in the VRF, not before.

C. Based on the Route Target.

The Route Target (RT) is a BGP extended community used to control the import and export of routes between different VRFs across the MPLS backbone, not for initial local association.

D. Based on the Service Identifier.

While a Service Identifier is used in the Nokia SR OS to configure and manage the VPRN service, the actual routing process associates the route based on the interface, which is a component of that service.

1. Nokia 7750 SR OS Services Guide, Release 21.10.R1, "VPRN Services" Chapter, Section: "VPRN Service Overview": This guide states, "A VPRN is created in the provider's network by creating a virtual routing and forwarding (VRF) instance on the PE routers for each VPRN. Each VPRN site must have one or more interfaces associated with it... When a PE router receives a packet from a CE router, it looks up the destination address in the VRF associated with the incoming interface." This confirms that the incoming interface dictates the VRF.

2. RFC 4364, "BGP/MPLS IP Virtual Private Networks (VPNs)", Section 4, "Operation": "A PE router can be attached to a number of CEs... A particular interface on the PE attaches it to a particular site. The PE's routing and forwarding tables for that site are known as 'per-site forwarding and routing tables'. The set of such tables for a particular site is a VRF." This foundational RFC establishes the principle of associating an interface with a VRF.