VPN service providers have traditionally kept their network topology private from IP-VPN customers, limiting interaction between them. This document proposes a Topology Abstraction (TA) service that provides controlled visibility of the service provider's network to VPNs. The TA service generates abstracted views of the network for each VPN accurately and fairly. Three decentralized schemes are developed to generate TAs with different performance characteristics, improving call performance for VPNs, fair resource sharing, and higher network utilization for the service provider. Simulation results validate the TA service concept and evaluate the proposed techniques over various network topologies.