HP HSR6800 Configuration Manual page 259

Figure 77 Network diagram for nested VPN
Propagation of routing information
In a nested VPN network, routing information is propagated as follows:
1. A provider PE and its CEs exchange VPNv4 routes, which carry information about users'
internal VPNs.
2. After receiving a VPNv4 route, a provider PE keeps the user's internal VPN information, and
appends the user's MPLS VPN attributes on the service provider network. That is, it replaces
the RD of the VPNv4 route with the RD of the user's MPLS VPN on the service provider network
and adds the export route-target (ERT) attribute of the user's MPLS VPN on the service
provider network to the extended community attribute list of the route. The internal VPN
information for the user 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 based on its
local VPNs. Each local VPN accepts routes of its own and advertises them to its connected
sub-VPN CEs (such as CE 3 and CE 4, or CE 5 and CE 6 in
a provider PE through an IPv4 connection, the PE advertises IPv4 routes to the CE. If a CE is
connected to a provider PE through a VPNv4 connection (a user MPLS VPN network), the PE
advertises VPNv4 routes to the CE.
Benefits
The nested VPN technology features the following main 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 levels of nesting of internal VPNs.
Nested VPN is flexible and easy to implement and can reduce the cost because a customer only
needs to pay for one MPLS VPN to have multiple internal VPNs connected. Nested VPN provides
diversified VPN networking methods for a customer, and allows for multi-level hierarchical access
control over the internal VPNs.
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Figure 77). If a CE is connected to