Juniper BGP - CONFIGURATION GUIDE V 11.1.X

because there are multiple tiers of VPNs—the tier-1 backbone VPN of the provider
carrier and the tier-2 VPNs of the customer carrier.
In a hierarchical carrier-of-carriers VPN environment, each carrier (or ISP) maintains
the internal routes of its customers in VRF tables on its PE routers. Therefore, the
customer carrier’s internal routes are installed into the VRF routing tables of the
provider carrier’s PE routers and advertised across the provider carrier’s core.
Similarly, the internal routes of the customer carrier’s customers are installed into
the VRF routing tables of the customer carrier’s PE routers. The customer carrier’s
external routing information is exchanged by its PE routers (which connect to the
provider carrier’s VPN) over their own IBGP session.
NOTE: To the customer carrier, the router it uses to connect to the provider carrier’s
VPN is a PE router. However, the provider carrier views this device as a CE router.
Carrier-of-carriers VPNs provide the following benefits to the customer carriers:
■ Reduced VPN administration—The VPN backbone is managed by the provider
carrier.
■ Reduced routing management—Intersite routing issues are the responsibility of
the provider carrier.
■ Flexibility—The VPN backbone can be used to deliver both VPN services and
Internet connectivity services.
The following benefits are provided to the provider carriers:
■ Reduced VPN administration—Provider carriers do not have to maintain separate
VPNs for each customer carrier’s end customer.
■ Reduced router management—Customer carriers manage their own CE routers.
■ Scalability—The provider carrier’s PE routers do not maintain the end customer’s
external routes (as required in a traditional networking environment); the
carrier-of-carriers network easily scales as the number of external routes and
VPNs increases.
The following sections describe the two types of carrier-of-carriers environments.
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.
470 ■ Carrier-of-Carriers IPv4 VPNs
JUNOSe 11.1.x BGP and MPLS Configuration Guide