Unexpected temporal and spatial changes of inter-AS routing behavior often lead to the necessity of on-demand inter-domain routingadjustment. For resolving this problem, we apply the AISLE framework, which is a multi-agent-based model, to a policy-based routingadjustment system for transit ISPs and their customer ASs. This paper describes the BGP-control architecture called VR (Virtual Router) that can dynamically change forwarding paths considering alternative paths, which are inferred from historical data and confirmed when they are actually applied. VR can control conventional multiple border routers in an AS without any protocol extensions. The policy description, which is interpreted by an agent, enables network operators to define autonomous actions for analyzing network status and adjusting inter-AS routing based on these observed results by issuing requests to VR. Some evaluation results indicate that VR can effectively change routing over BGP data on the actual Internet and some control scenarios based on policy descriptions demonstrate the validity of our basic design framework.