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 VLAN (Virtual LAN)s, 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.
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