An efficient approach to solve scalability problem of current inter-domain routing system is to separate the edge network from the core network address space. But the approach based on core-edge separation needs a new mapping service system to distribute transition information between core and edge networks address spaces through Internet. And after separating and mapping, it needs a method to ensure it is backwards compatible with the current addressing and routing architecture. Aiming to the problem caused by mapping service and compatibility, this paper proposes a scalable inter-domain routing architecture, called SIRAS. SIRAS reuses IPv4 address space to ensure backwards compatibility, and avoids introducing a new mapping service system by extending existing DNS and protocols. The analysis shows SIRAS efficiently alleviates scalability pressure without introducing a new mapping service and protocol.