3com S7906E Installation Instruction

 

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The nested VPN technology simplifies the complexity for a user to access a VPN, reduces the access 

cost, supports diversified VPN networking methods, and implements control over the access to internal 

VPNs and control over mutual access among multiple levels of VPNs. 

1)  Hierarchical model and plane model 

In MPLS L3VPN solutions, PEs are the key devices. They provide two functions: 

z 

User access. This means that the PEs must have a large amount of interfaces. 

z 

VPN route managing and advertising, and user packet processing. These require that a PE must 

have a large-capacity memory and high forwarding capability. 

Most of the current network schemes use the typical hierarchical architecture. For example, the MAN 

architecture contains typically three layers, namely, the core layer, convergence layer, and access layer. 

From the core layer to the access layer, the performance requirements on the devices reduce while the 

network expands. 

MPLS L3VPN, on the contrary, is a plane model where performance requirements are the same for all 

PEs. If a certain PE has limited performance or scalability, the performance or scalability of the whole 

network is influenced. 

Due to the above difference, you are faced with the scalability problem when deploying PEs at any of 

the three layers. Therefore, the plane model is not applicable to the large-scale VPN deployment. 

2) HoVPN 

To solve the scalability problem of the plane model, MPLS L3VPN must transition to the hierarchical 

model. 

In MPLS L3VPN, hierarchy of VPN (HoVPN) was proposed to meet that requirement. With HoVPN, the 

PE functions can be distributed among multiple PEs, which take different roles for the same functions 

and form a hierarchical architecture. 

As in the typical hierarchical network model, HoVPN has different requirements on the devices at 

different layers of the hierarchy. 

1)  Basic architecture of HoVPN