SUMMARYMultipath routing has been extended to Border Gateway Protocol (BGP), the current de facto inter-domain routing protocol, to address the reliability and performance issues of the current Internet. However, inter-domain multipath routing introduces a significant challenge for scalability due to the large scale of the inter-domain routing system. At the same time it also introduces new challenges in terms of security and security related overhead. In this paper, we propose a regional multipath approach, Regional Multipath Inter-domain Routing (RMI), where multiple paths are only allowed to be propagated within a well-defined range. With multipath routing in a region, we enable inter-domain routing with rich path diversity and improved security, and no longer have to sacrifice scalability. We show how to propagate multiple paths based on the region by theoretical analysis and by extensive simulations. Our simulations show that the number of messages generated using this approach and the convergence delay are much less than those of BGP and BGP with full multipath advertisement.