# Customer Carrier as an Internet Service Provider

The provider carrier’s VPN can function as the backbone for a customer carrier that provides Internet services for its customers at multiple sites. In this type of carrier-of-carriers environment, MPLS label-switched paths are established among the customer carrier’s PE routers that connect to the provider carrier at each site. Routes are learned and maintained as follows:

- The customer carrier’s internal routes are learned and advertised across the provider carrier’s VPN. The customer carrier’s external routes are not installed in the provider’s VPN.
- The customer carrier’s PE routers that connect to the provider’s VPN use LDP to exchange labels for the internal routes between themselves and the provider carrier’s PE router.
- The customer carrier’s PE routers that connect to the provider’s VPN learn external routes through IBGP sessions among themselves.

Figure 109 shows a sample carrier-of-carriers environment in which the customer carrier provides Internet connectivity services to its customers. The figure shows how the labels are added and removed as the traffic traverses the network. The label-signaling protocol is assumed to be LDP.

Figure 109: Carrier-of-Carriers Internet Service