H3C Technologies H3C S12500-X Series Switches - Manual (Page 123)

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Figure 41 Network diagram for nested VPN
Propagation of routing information
In a nested VPN network, routing information is propagated by using the following process:
1. A provider PE and its CEs exchange VPNv4 routes, which carry information about customer VPNs.
2. After receiving a VPNv4 route, a provider PE keeps the customer's internal VPN information, and
appends the customer's MPLS VPN attributes on the service provider network. It replaces the RD of
the VPNv4 route with the RD of the customer's MPLS VPN on the service provider network. It also
adds the export route-target (ERT) attribute of the customer's MPLS VPN on the service provider
network to the extended community attribute list of the route. The internal VPN information for the
customer is maintained on the provider PE.
3. The provider PE advertises VPNv4 routes carrying the comprehensive VPN information to the other
PEs of the service provider.
4. After another provider PE receives the VPNv4 routes, it matches the VPNv4 routes to the import
targets of its local VPNs. Each local VPN accepts routes of its own and advertises them to provider
CEs. If a provider CE (such as CE 7 and CE 8 in Figure 41 ) is connected to a provider PE through
an IPv4 connection, the PE advertises IPv4 routes to the CE. If it is a VPNv4 connection (a customer
MPLS VPN network), the PE advertises VPNv4 routes to the CE.
5. After receiving VPNv4 routes from the provider CE, a customer PE matches those routes to local
import targets. Each customer VPN accepts only its own routes and advertises them to connected
customer CEs (such as CE 3, CE 4, CE 5, and CE 6 in Figure 41 ).
Benefits
The nested VPN technology provides the following benefits:
• Support for VPN aggregation. It can aggregate a customer's internal VPNs into one VPN on the
service provider's MPLS VPN network.
• Support for both symmetric networking and asymmetric networking. Sites of the same VPN can
have the same number or different numbers of internal VPNs.
• Support for multiple-level nesting of internal VPNs.
Provider PE
CE 3 CE 4
Provider MPLS
VPN backbone
P
VPN A-1
VPN A-1 VPN A-2
CE 7
Provider PE
VPN A-2
CE 8
Customer MPLS
VPN
Customer PE
CE 5 CE 6
VPN A-1 VPN A-2
Customer MPLS
VPN network
Customer PE
CE 1 CE 2
VPN A