"A collection of interconnected networks" defines what the Internet is, but not what it is not. Events threaten Internet fragmentation: politics suggest countries or ISPs may secede or be de-peered, disputes between ISPs result in persistent unreachability between their customers, and architectural changes risk breaking the "one" Internet. Understanding such threats benefits from a testable definition of what the Internet is and is not, enabling discussion and quantification of partial connectivity. We provide a conceptual definition giving an idealized asymptote of connectivity. It implies peninsulas of persistent, partial connectivity, and islands when one or more computers are partitioned from the main Internet. We provide algorithms to measure, operationally, the number, size, and duration of peninsulas and islands. We apply these algorithms in rigorous measurement from two complementary measurement systems, one observing 5M networks from a few locations, and the other a few destinations from 10k locations. Results show that peninsulas (partial connectivity) are about as common as Internet outages, quantifying this long-observed problem. Root causes show that most peninsula events (45%) are routing transients, but most peninsula-time (90%) is from a few long-lived events (7%). Our analysis helps interpret DNSmon, a system monitoring the DNS root, separating measurement error and persistent problems from underlying differences and operationally important transients. Finally, our definition confirms the international nature of the Internet: no single country can unilaterally claim to be "the Internet", but countries can choose to leave.

翻译："互联网络的集合"定义了互联网是什么，但并未定义其不是什么。某些事件威胁着互联网的碎片化：政治因素表明国家或互联网服务提供商可能退出或被取消对等互联，互联网服务提供商之间的争端导致其用户之间的持续不可达性问题，而架构上的变化则可能破坏"单一"互联网。理解此类威胁需要一个可检验的定义，明确互联网是什么及其不是什么的边界，从而能够讨论和量化部分连通性。我们提出了一个概念性定义，给出了一个理想化的连通性渐近线。该定义对应着持续存在部分连通性的"半岛"，以及当一台或多台计算机与主互联网断开连接时形成的"孤岛"。我们提供了算法来从操作层面测量半岛和孤岛的数量、规模和持续时间。我们通过两种互补的测量系统严格应用这些算法：一个系统从少数位置观测500万个网络，另一个系统从1万个位置观测少数目标。结果表明，半岛（部分连通性）与互联网中断的发生频率大致相同，从而量化了这一长期被观察到的问题。根本原因分析显示，大多数半岛事件（45%）是由路由瞬态导致的，但绝大多数半岛时间（90%）来自少数长期存在的事件（7%）。我们的分析有助于解读DNSmon——一个监控DNS根区的系统，能够将测量误差和持久性问题与底层差异及操作上重要的瞬态区分开来。最后，我们的定义证实了互联网的国际性：没有任何国家可以单方面宣称自己就是"互联网"，但各国可以选择退出。