Inter-Autonomous System Connectivity: Another Application of Tunnels
Carrier Supporting Carrier Carrier supporting carrier (CsC) is a two-layer IP VPN solution designed to allow a backbone carrier to use MPLS VPN (or L2TPv3) to carry traffic belonging to customers' carriers that use MPLS VPNs. Before looking at the solution, it is a good idea to understand the problem being solved . An MPLS PE router holds all the routes of all the sites to which it connects. In a normal scenario, although this number can be large, the expectation is that an individual VPN would require at most hundreds or perhaps thousands of entries in a VRF. However, if the customer is itself an ISP, carrying routes belonging to their customers, the potential exists to require the backbone PE to carry an impossibly large number of routes. The CsC solution addresses this issue. CsC is based on the observation that the label switched domain of an MPLS VPN network (that is, the backbone network) on...