3Com S7906E - Switch, Configuration Manual

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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.
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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.
Figure 1-1 shows the MPLS L3VPN model.
Figure 1-1 Network diagram for MPLS L3VPN model
VPN 1
CE
Site 1
VPN 2
CE
CE
CE
Site 3
VPN 2
PE
VPN 1
Site 2
Site 4
PE
PE
P P
P P
CEs and PEs mark the boundary between the service providers and the customers.
A CE is usually a router. After a CE establishes adjacency with a directly connected PE, it advertises its
VPN routes to the PE and learns remote VPN routes from the PE. A CE and a PE use BGP/IGP to
exchange routing information. You can also configure static routes between them.
After a PE learns the VPN routing information of a CE, it uses BGP to exchange VPN routing
information with other PEs. A PE maintains routing information about only VPNs that are directly
connected, rather than all VPN routing information on the provider network.
A P router maintains only routes to PEs. It does not need to know anything about VPN routing
information.
When VPN traffic travels over the MPLS backbone, the ingress PE functions as the ingress LSR, the
egress PE functions as the egress LSR, while P routers function as the transit LSRs.
MPLS L3VPN Concepts
Site
Site is often mentioned in the VPN. Its meanings are described as follows:
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A site is a group of IP systems with IP connectivity that does not rely on any service provider
network to implement.
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The classification of a site depends on the topology relationship of the devices, rather than the
geographical positions, though the devices at a site are adjacent to each other geographically in
most cases.
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The devices at a site can belong to multiple VPNs.
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A site is connected to a provider network through one or more CEs. A site can contain many CEs,
but a CE can belong to only one site.