3Com S7906E - Switch, Руководство по настройке

Страница: 1481 / 2621

1-2
MPLS L2VPN transfers Layer 2 user data transparently on the MPLS network. For users, the MPLS
network is a Layer 2 switched network and can be used to establish Layer 2 connections between
nodes.
Consider ATM as an example. Each customer edge device (CE) can connect to the MPLS network
through an ATM virtual circuit (VC) to communicate with another CE. This is similar to that on an ATM
network.
Figure 1-1 Network diagram for MPLS L2VPN
Comparison with MPLS L3VPN
Compared with MPLS L3VPN, MPLS L2VPN has the following advantages:
z
High scalability: MPLS L2VPN establishes only Layer 2 connections. It does not involve the routing
information of users. This greatly reduces the load of the PEs and even the load of the whole
service provider network, enabling carriers to support more VPNs and to service more users.
z
Guaranteed reliability and private routing information security: As no routing information of users is
involved, MPLS L2VPN neither tries to obtain nor processes the routing information of users,
guaranteeing the security of the user VPN routing information.
z
Support for multiple network layer protocols, such as IP, IPX, and SNA.
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:
z
Customer edge device (CE): A CE resides on a customer network and has one or more interfaces
directly connected with service provider networks. It can be a router, a switch, or a host. It cannot
"sense" the existence of any VPN, neither does it need to support MPLS.
z
Provider edge router (PE): A PE resides on a service provider network and connects one or more
CEs to the network. On an MPLS network, all VPN processing occurs on the PEs.
z
Provider (P) router: A P router is a backbone router on a service provider network. It is not directly
connected with any CE. It only needs to be equipped with basic MPLS forwarding capability.
MPLS L2VPN uses label stacks to implement the transparent transmission of user packets in the MPLS
network.
z
Outer label, also called tunnel label, is used to transfer packets from one PE to another.
z
Inner label, also called VC label, is used to identify different connections between VPNs.