The promise of decentralized peer-to-peer (P2P) systems is fundamentally gated by the challenge of Network Address Translation (NAT) traversal, with existing solutions often reintroducing the very centralization they seek to avoid. This paper presents the first large-scale measurement study of a fully decentralized NAT traversal protocol, Direct Connection Upgrade through Relay (DCUtR), within the production libp2p-based InterPlanetary File System (IPFS) network. Drawing on over 4.4 million traversal attempts from 85,000+ distinct networks across 167 countries, we provide an empirical analysis of modern P2P connectivity. We establish a conditional success rate of $70\% \pm 7.1\%$ for the hole-punching stage, given that prerequisite relay reservation and public address discovery succeed, providing a crucial new benchmark for the field. Critically, we empirically challenge the long-held belief of UDP's superiority for NAT traversal, demonstrating that DCUtR's high-precision, RTT-based synchronization yields statistically indistinguishable success rates for both TCP and QUIC ($\sim70\%$). Our analysis further validates the protocol's design for permissionless environments by showing that success is independent of relay characteristics and that the mechanism is highly efficient, with $97.6\%$ of successful connections established on the first attempt. Building on this analysis, we propose a concrete roadmap of protocol enhancements aimed at achieving universal connectivity and contribute our complete dataset to foster further research in this domain.

翻译：去中心化对等（P2P）系统的前景从根本上受限于网络地址转换（NAT）穿透的挑战，现有解决方案往往重新引入了其试图避免的中心化。本文首次对基于libp2p的星际文件系统（IPFS）生产网络中完全去中心化的NAT穿透协议——通过中继的直接连接升级（DCUtR）——进行了大规模测量研究。基于来自167个国家85000多个不同网络的超过440万次穿透尝试，我们提供了对现代P2P连接性的实证分析。在前提条件（中继预留和公网地址发现）成功的情况下，我们确定打洞阶段的成功率为$70\% \pm 7.1\%$，为该领域提供了关键的新基准。至关重要的是，我们通过实证挑战了UDP在NAT穿透中具有优越性的长期观点，证明DCUtR基于高精度RTT的同步机制使得TCP和QUIC的成功率在统计上无显著差异（均约为$70\%$）。我们的分析进一步验证了该协议在无许可环境中的设计合理性：成功率与中继特性无关，且该机制高度高效——$97.6\%$的成功连接在首次尝试中建立。基于此分析，我们提出了旨在实现通用连接性的协议增强具体路线图，并贡献了完整数据集以促进该领域的进一步研究。