MCE overview

BGP/MPLS VPN transmits private network data through MPLS tunnels over the public network. However, the traditional MPLS L3VPN architecture requires that each VPN instance use an exclusive CE to connect to a PE, as shown in Figure 92.

A private network is usually divided into multiple VPNs to isolate services. To meet these requirements, you can configure a CE for each VPN, which increases device expense and maintenance costs. Or, you can configure multiple VPNs to use the same CE and the same routing table, which sacrifices data security.

You can use the Multi-VPN-Instance CE (MCE) function in multi-VPN networks. MCE allows you to bind each VPN to a VLAN interface. The MCE creates and maintains a separate routing table for each VPN. This separates the forwarding paths of packets of different VPNs and, in conjunction with the PE, can correctly advertise the routes of each VPN to the peer PE, ensuring the normal transmission of VPN packets over the public network.

As shown in Figure 94, the MCE device creates a routing table for each VPN. VLAN interface 2 binds to VPN 1 and VLAN-interface 3 binds to VPN 2. When receiving a route, the MCE device determines the source of the routing information according to the number of the receiving interface, and then adds it to the corresponding routing table. The MCE connects to PE 1 through a trunk link that permits packets tagged with VLAN 2 or VLAN 3. PE 1 determines the VPN that a received packet belongs to according to the VLAN tag of the packet, and sends the packet through the corresponding tunnel.

You can configure static routes, RIP, OSPF, IS-IS, EBGP, or IBGP between an MCE and a VPN site and between an MCE and a PE.

	NOTE: To implement dynamic IP assignment for DHCP clients in private networks, you can configure DHCP server or DHCP relay agent on the MCE. When the MCE functions as the DHCP server, the IP addresses assigned to different private networks cannot overlap.