As a promising network-based mobility management method that does not require active participation of mobile nodes (MNs), Proxy Mobile IPv6 (PMIPv6) is attracting considerable attention among the telecommunication and Internet communities. It remains an open issue how to build a scalable PMIPv6 domain that is able to support a large number of MNs while keeping handover delays low. In this paper, we propose an approach for building Scalable And Robust PMIPv6 (SARP) domains. We propose that every mobility access gateway (MAG) in a SARP domain also functions as a local mobility anchor (LMA), and is organized into a virtual ring with all other MAGs. Consistent hashing is used to efficiently distribute the mapping between each MN and its LMA to all MAGs. A MAG finds an MN's LMA by sending a query message to the virtual ring. Our analysis verifies the robustness and scalability of SARP. We also propose two handover procedures for SARP and show that they achieve low handover delays.