The Internet was originally defined as "a collection of inter-connected networks". While this definition helps us understand what the Internet is, it is silent on when the Internet is not. We provide a testable definition of the Internet to clarify where the Internet "ends": disconnection when a country or an ISP secedes; persistent partial connectivity when major ISPs refuse to exchange traffic, isolating their customers; clarifying corner cases around carrier-grade NAT, unrouted public IP addresses, and interpreting conflicting observations from systems that detect Internet outages. Our definition identifies peninsulas of persistent, partial connectivity, and clarifies that outages are islands, with internal connectivity that is partitioned from the main Internet. Our definition is conceptual, defining an ideal asymptote of connectivity, but it enables new algorithms that provide an operational estimate of the number of size of peninsulas and islands. We use these algorithms to reinterpret data from two existing measurement systems, one covering 5 million /24 IPv4 networks and the other with 10k observers. A key result is that peninsulas are about as common as outages, newly clarifying the importance of this long-observed problem. We examine root causes, showing that most peninsula events (45%) are transient routing problems, but a few long-lived peninsulas events (7%) account for 90% of all peninsula time, suggesting country- or AS-level policy choices that last weeks or more. Finally, our definition confirms the international nature of internet: no single country can unilaterally claim to be "the Internet", but countries can chose to leave. With islands and peninsulas, our definition helps clarify the spectrum from partial reachability to outages in prior work.

翻译：互联网最初被定义为“ 内部连接网络的集合 ” 。 虽然这一定义有助于我们理解互联网是什么, 但当互联网不是互联网的时候, 互联网是沉默的。 我们提供了一个互联网的可测试的定义, 以澄清互联网“ 结束 ” : 当一个国家或互联网服务供应商分离时, 断开; 当主要的互联网服务供应商拒绝交换交通, 孤立其客户时, 持续地部分连接; 澄清承运人级NAT、 无路由的公共IP地址周围的角落案例, 并解释从检测互联网断流的系统中得出的相互矛盾的观测结果。 我们的定义确定了持续、部分连接的半岛, 并澄清了离线是岛屿, 内部连接与主要互联网隔绝。 我们的定义是概念性的, 定义一个理想的连接点是连接, 但它使得新的算法能够提供对半岛和岛屿数量的实际估计。 我们使用这些算法从两个现有的测量系统, 一个覆盖500万个部分 IPv4 网络,另一个覆盖10k观察者。 一个关键的结果是, 半岛作为共同的距离是岛屿,,,,, 最终的互联网连接是,,,, 最终的路径,,, 意味着,, 从这个半岛国家( ),,, 最终的,,,,,,,,,,, 从一个是, 从一个是,,, 从一个是,,,,,,, 到,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,