The customer of a VPN service provider might be a service provider for the end customer. The following are the two main types of carrier-of-carriers VPNs (as described in RFC 4364:
Figure 50 illustrates the network architecture used for a carrier-of-carriers VPN service.
Figure 50: Carrier-of-Carriers VPN Architecture
In this type of carrier-of-carriers VPN configuration, ISP A configures its network to provide Internet service to ISP B. ISP B provides the connection to the customer wanting Internet service, but the actual Internet service is provided by ISP A.
This type of carrier-of-carriers VPN configuration has the following characteristics:
A VPN service provider can have customers that are themselves VPN service providers. In this type of configuration, also called a hierarchical or recursive VPN, the customer VPN service provider’s VPN-IPv4 routes are considered external routes, and the backbone VPN service provider does not import them into its VRF table. The backbone VPN service provider imports only the customer VPN service provider’s internal routes into its VRF table.
This type of configuration is similar to the configuration described in the Internet Service Provider as the Customer section. The similarities and differences are shown in Table 14.
Table 14: Comparison of Interprovider and Carrier-of-Carriers VPNs
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