3Com S7902E, Руководство по настройке

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Figure 1-12 Scenario where the Level 2 carrier is an MPLS L3VPN service provider
If there are equal cost routes between the Level 1 carrier and the Level 2 carrier, you are recommended
to establish equal cost LSPs between them accordingly.
Nested VPN
Background
In an MPLS L3VPN network, generally a service provider runs an MPLS L3VPN backbone and provides
VPN services through PEs. VPN users are connected to PEs through CEs to access the MPLS L3VPN
network. In this way, users in the same VPN at different sites can communicate with each other. In this
scenario, user networks are ordinary IP networks and cannot be further divided into sub-VPNs.
However, in actual applications, VPN user networks can be dramatically different in form and complexity,
and a VPN user network may need to use VPNs to further group its users. The traditional solution to this
request is to implement internal VPN configuration on the service provider’s PEs. This solution is easy
to deploy, but it increases the network operation cost and brings issues on management and security
because:
z
The number of VPNs that PEs must support will increase sharply.
z
Any modification of an internal VPN must be done through the service provider.
The nested VPN technology offers a better solution. Its essence is to exchange VPNv4 routes between
PEs and CEs of an ordinary MPLS L3VPN, and to allow VPN users to manage their own internal VPNs.
Figure 1-13 depicts a nested VPN network. On the service provider’s MPLS VPN network, there is a
user VPN named VPN A. The user VPN contains two sub-VPNs, VPN A-1 and VPN A-2. The service
provider PEs treat the user network as a common VPN user and will not join any sub-VPNs. The VPN
user’s CE devices (CE 1, CE 2, CE 7 and CE 8) exchange VPNv4 routes that carry the sub-VPN routing
information with the service provider PEs, implementing the propagation of the sub-VPN routing
information throughout the user network.