How Shared Services in MPLS Layer 3 VPN Provide Internet Access to Customers

C.

In an MPLS Layer 3 VPN, a central service provider offers VPN services to multiple customers. The provider needs to provide Internet access to its customers using shared services. There are several ways to accomplish this, but the most common methods are described below:

A. Static routes on CE routers allow route leakage from a PE global routing table. This approach involves configuring static routes on the customer edge (CE) routers to leak routes from the provider edge (PE) router's global routing table. This method can be inefficient because it requires manual configuration of the static routes on the CE routers, which can be difficult to maintain as the network grows.

B. The CE router can establish a BGP peering to a PE router and use the PE device to reach the Internet. This method involves configuring the CE router to establish a BGP peering with the PE router and use the PE router as the default gateway to reach the Internet. The provider must configure the PE router to advertise default routes to the customer, and the customer must configure its CE router to accept the default routes.

C. The customer virtual routing and forwarding (VRF) uses route targets to import and export routes to and from a shared services VR. This method involves creating a separate VRF on the provider's PE router that is shared by all customers who require Internet access. The provider configures the shared services VRF to import and export Internet routes using route targets. The customer VRFs import routes from the shared services VRF to provide Internet access to their networks.

D. Route distinguishers are used to identify the routes that CEs can use to reach the Internet. This method is similar to method A, but instead of using static routes, the provider uses route distinguishers to identify the routes that the CE routers can use to reach the Internet. The provider configures the PE routers to advertise routes with the appropriate route distinguishers to the CE routers.

Overall, methods B and C are the most commonly used for providing Internet access to customers of a central service provider. Method B is simpler to configure, but method C provides more flexibility and scalability as the network grows.