We present the design and evaluation of I4, a network infrastructure that enables information exchange and collaboration among different domains. I4 can help with network management in many scenarios, such as when eliminating the unwanted traffic to improve the network performance as well as diagnosing the network problems. We present the Distributed Denial-of-Service (DDoS) attack as an example to demonstrate the advantages of I4. Simulation results show that I4 can significantly reduce the amount of DDoS attack packets and dramatically improve the quality of services received by legitimate users. Our design provides attractive properties, such as incremental deployment as well as incentives for such deployment etc.