Towards Option-Based IPv4 Address Extension: A Measurement Study and Testbed Deployment

The prolonged coexistence of IPv4 and IPv6 motivates exploring whether IPv4 can be extended beyond its 32-bit address limitation. IPswen encodes variable-length addresses within standard IPv4 options, allowing legacy routers to forward packets based on the 32-bit base address without modification. However, whether such option-bearing packets can traverse the real Internet remains empirically unvalidated. This paper presents the first large-scale measurement of unknown IPv4 option reachability across approximately 75,000 ASes from four geographically distributed vantage points. We find that options ≥ 8 bytes achieve 38–64% reachability across core Internet paths, with bounded RTT overhead under 32%. Motivated by this partial reachability, we design a pragmatic deployment model centered on domain-controlled WAN overlays: native forwarding where options pass, with automatic GRE-based fallback where they do not. We implement this model in a multi-continent testbed featuring Automatic Tunnel Switching, a BGP Virtual Direct Connection scheme for route distribution, and an extended Linux kernel FIB supporting variable-length prefixes. Our evaluation demonstrates acceptable control-plane convergence overhead and data-plane scalability up to 10M routes, establishing a concrete platform for studying incremental IPv4 evolution.