Deployments of Multiprotocol Label Switching (MPLS) have become routine in large-scale global networks, which demand solutions to complex business and network problems. There are two primary components of the Cisco IOS MPLS Inter-Domain Solution: Inter-AS and Carrier Supporting Carrier.
Inter-AS is a peer-to-peer type model that allows extension of VPNs through multiple provider or multi-domain networks. This solution enables Service Providers to peer up with one another and offer end-to-end VPN connectivity over extended geographical locations for those subscribers who may be out of reach for a single provider.
Carrier Supporting Carrier (CSC) is a hierarchical VPN model that allows small Service Providers, or customer carriers, to interconnect their IP or MPLS networks over an MPLS backbone. This eliminates the need for customer carriers to build and maintain their own MPLS backbone.
Both Inter-AS and CSC can construct scalable networks that help maintain network segmentation based on internal organizational or operational boundaries.