Multiple Forwarding Tables
Each PE router needs to maintain one forwarding table per VPN that it is directly connected. These forwarding tables are called Virtual Routing and Forwarding tables (VRF). When a PE router is configured, each of it‘s VRF is associated with one or more VLANs, that is, there is a many to one mapping from VLAN to VPN/VRF. When receiving inbound data traffic from a directly attached CE router, PE router determines the VRF for the packet based on which VLAN the packet has been received. The ingress VLAN will uniquely map to a particular VRF in the system. Then, PE router performs a route lookup for the packet‘s destination IP address in the associated VRF. In the figure above, both PE1 and PE3 have two VRFs, one each for VPN-A and VPN-B, whereas, PE2 has only one VRF which is for VPN-A.