Operation Manual – NAT-URPF-VPLSH3C S9500 Series Routing Switches Chapter 3 VPLS Configuration3-3Figure 3-2 Hierarchical VPLS network architectureAs shown in Figure 3-2, the network topology of the VPLS network is hierarchical, andthe access range of the network is expansible. The core devices (NPEs) in the corenetwork require high performance because VPN traffic concentrates there, while theedge devices (UPEs) require lower performance because they are mainly used for VPNservice access. In addition, you can back up the links between NPEs and UPEs tomake the network more robust. The access networks between UPEs and NPEs can beeither a MPLS edge network connected by LSP, or a simple Ethernet network forVLAN-VPN user access.3.3 VPLS Operational Principle3.3.1 VPLS Basic Transmission ComponentsAs shown in the following figure, the whole VPLS network is just like a huge switch. Foreach VPN, it sets up PWs between the sites of the VPN on MPLS tunnels andtransparently transmits user's layer 2 packets from one site to another through thesePWs. In this network, PEs forward packets, learn source MAC addresses, create MACforwarding entries, and map the MAC addresses to corresponding ACs and PWs.While, the P devices (provider routers, that is, core switches in the backbone network),only implement MPLS forwarding according to MPLS labels without considering layer 2user data encapsulated in MPLS packets.
