14-6By establishing multiple tunnels between two MCE devices and binding the tunnel interfaces with VPNinstances, you can make the routing information and data of the VPN instances delivered to the peerdevices through the bound tunnel interfaces. According to the tunnel interfaces receiving the routes, anMCE devices determine the VPN instances that the routes belong to and advertise the routes to thecorresponding sites. As shown in Figure 14-4, you can bind Tunnel 1 with VPN 1 to make the MCEdevices deliver the routing information and data of VPN 1 through the tunnel.An MCE can also be used in a tunneling application as shown in Figure 14-5 to connect with multipleremote CEs through tunnels. In this scenario, the CE devices only need to receive and advertiseroutes as usual, while the MCE advertises and receives VPN routing information based on thebindings between tunnel interfaces and VPNs.Figure 14-5 Network diagram for using MCE in a tunneling application (2)z MCE devices in a tunneling application can exchange VPN routing information with their peerMCE devices or CE devices directly, just as MCE devices in an MPLS L3VPN application do withthe corresponding PEs. For details, refer to Route Exchange between MCE and PE.z Currently, these types of tunnels support MCE: GRE tunnel, IPv4 over IPv4 tunnel, and IPv4 overIPv6 tunnel.z For introduction and configuration of tunnel types, see Tunneling Configuration in the Layer 3 - IPServices Configuration Guide.Routing Information Exchange for MCEInterface-to-VPN-instance binding enables MCEs and PEs to determine the sources of receivedpackets and then forward the packets according to the routing information concerning thecorresponding VPNs. The following sections describe the way how MCE transmits the private routinginformation of multiple VPNs to PEs properly.Route Exchange between an MCE and the Private NetworkAn MCE can adopt the following routing protocols to exchange VPN routes with a site:
