The following components, as shown in the diagram below, comprise a BGP or MPLS VPN.
Customer Edge device (CE)—The CE provides connectivity with a customer‘s network and a Provider Edge device (PE). It can advertise routes available from the customer‘s network using RIP, OSPF or EBGP. Alternately, the CE can create a static default route to a PE. Outbound packets from a customer‘s network are forwarded from the CE to the PE, and inbound packets are forwarded from the PE to the CE attached to the customer‘s network.
Provider Edge device (PE)—In a BGP or MPLS VPN, the central component is the PE. The PE provides connectivity with the CE and with the MPLS domain. On one side of the PE, routing information is exchanged with the CE using either static routes, RIP, OSPF, or EBGP. On the other side, IBGP is used with BGP multiprotocol extensions to communicate with all of the other PEs that are connected to networks in the same VPN and available to the customer‘s network. When a CE sends packets to a PE to forward across an MPLS domain, that PE functions as an MPLS ingress Label Edge router (LER) and the PE on the other end of the domain functions as an MPLS egress LER.
Virtual Routing and Forwarding table (VRF)—Virtual Routing and Forwarding table (VRF) - The PE maintains a Virtual Routing and Forwarding table (VRF) for each customer that is attached to it through a CE. The VRF contains routes between the PE and the CE and
Label Switched Paths (LSPs) across the MPLS domain for each PE that is a member of the customer‘s VPN. VRFs are defined on interfaces of the PEs.
Provider MPLS domain—The Provider MPLS domain is composed of Provider (P) devices. An MPLS domain can traverse more than one service provider‘s MPLS network. The P devices do not store any VPN information; they just switch traffic from the ingress PE device along the LSP to the egress PE device.
