Routing strives to connect all the Internet, but compete: political pressure threatens routing fragmentation; architectural changes such as private clouds, carrier-grade NAT, and firewalls make connectivity conditional; and commercial disputes create partial reachability for days or years. This paper suggests *persistent, partial reachability is fundamental to the Internet* and an underexplored problem. We first *derive a conceptual definition of the Internet core* based on connectivity, not authority. We identify *peninsulas*: persistent, partial connectivity; and *islands*: when computers are partitioned from the Internet core. Second, we develop algorithms to observe each across the Internet, and apply them to two existing measurement systems: Trinocular, where 6 locations observe 5M networks frequently, and RIPE Atlas, where 13k locations scan the DNS roots frequently. Cross-validation shows our findings are stable over *three years of data*, and consistent with as few as 3 geographically-distributed observers. We validate peninsulas and islands against CAIDA Ark, showing good recall (0.94) and bounding precision between 0.42 and 0.82. Finally, our work has broad practical impact: we show that *peninsulas are more common than Internet outages*. Factoring out peninsulas and islands as noise can *improve existing measurement systems*; their ``noise'' is $5\times$ to $9.7\times$ larger than the operational events in RIPE's DNSmon. We show that most peninsula events are routing transients (45\%), but most peninsula-time (90\%) is due to a few (7\%) long-lived events. Our work helps inform Internet policy and governance, with our neutral definition showing no single country or organization can unilaterally control the Internet core.

翻译：路由旨在连接整个互联网，但现实中的竞争因素使其面临挑战：政治压力威胁着路由碎片化；私有云、运营商级NAT和防火墙等架构变革使连通性变得有条件；商业争端则导致持续数天乃至数年的部分可达性问题。本文提出*持久性部分可达性是互联网的基本特征*，且是一个尚未被充分探索的问题。我们首先*基于连通性而非权威性推导出互联网核心的概念定义*，识别出*半岛*（即持久性部分连通区域）与*孤岛*（即与互联网核心隔离的计算节点群）。其次，我们开发了观测互联网中这两类现象的算法，并将其应用于两个现有测量系统：Trinocular（6个观测点对500万网络进行高频监测）和RIPE Atlas（1.3万个观测点高频扫描DNS根服务器）。交叉验证表明，我们的发现在*三年数据*中保持稳定，且仅需3个地理分散的观测点即可保持一致性。通过CAIDA Ark数据验证半岛与孤岛现象，我们获得了良好的召回率（0.94），并将精确度界定在0.42至0.82之间。最后，本研究具有广泛的实际影响：我们证明*半岛现象比互联网中断更常见*。将半岛和孤岛视为噪声进行过滤可*改进现有测量系统*——在RIPE的DNSmon系统中，这类“噪声”的规模是运营事件的$5$倍至$9.7$倍。数据显示多数半岛事件属于路由瞬态现象（45%），但半岛状态的持续时间（90%）主要由少数（7%）长时事件主导。本研究为互联网政策与治理提供了新视角：我们提出的中立定义表明，任何单一国家或组织都无法单方面控制互联网核心。