H3C Technologies H3C SR8800 - Manual (Page 201)

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Basic concepts of MPLS L2VPN
In MPLS L2VPN, the concepts and principles of CE, PE and P are the same as those in MPLS L3VPN:
• Customer edge (CE) device—A CE resides on a customer network and has one or more interfaces
directly connected to service provider networks. It can be a router, a switch, or a host. It can neither
“sense” the presence of any VPN nor does it need to support MPLS.
• Provider edge (PE) device—A PE resides at the edge of a service provider network and connects
one or more CEs. On an MPLS network, all VPN services are processed on the PEs.
• Provider (P) device—A P device is a core device on a service provider network. It is not directly
connected to any CE. It has only basic MPLS forwarding capability.
MPLS L2VPN uses label stacks to implement the transparent transmission of user packets in the MPLS
network.
• Outer label, also called tunnel label, is used to transfer packets from one PE to another.
• Inner label, also called VC label, is used to identify different connections between VPNs.
• Upon receiving packets, a PE determines to which CE the packets are to be forwarded according
to the VC labels.
Figure 48 illustrates how the label stack changes in the MPLS L2VPN forwarding process.
Figure 48 MPLS L2VPN label stack processing
1) L2 PDU: Layer 2 protocol data unit
2) T represents tunnel label. V represents VC label. T’ represents swapped tunnel label.
Implementation of MPLS L2VPN
MPLS L2VPN can be implemented in one of the following methods:
• Circuit Cross Connect (CCC) and Static Virtual Circuit (SVC)—Two methods of implementing MPLS
L2VPN by configuring VC labels statically.
• Martini—A method for establishing PPP links to implement MPLS L2VPN. It uses Label Distribution
Protocol (LDP) as a signaling protocol to transfer VC labels.
• Kompella—A CE-to-CE mode for implementing MPLS L2VPN on the MPLS network. It uses extended
BGP as the signaling protocol to advertise Layer 2 reachability information and VC labels.
The following sections describe these implementation methods for MPLS L2VPN in detail.