What Is The Internet? Partial Connectivity in the Internet Core

TL;DR

This paper offers a formal definition of the Internet's connectivity, introduces algorithms to measure partial connectivity phenomena like peninsulas and islands, and provides empirical data on their prevalence and causes.

Contribution

It presents a testable, conceptual definition of Internet connectivity and algorithms for measuring partial connectivity, validated through large-scale measurements.

Findings

Peninsulas of partial connectivity are as common as outages.

Most peninsula-time is due to a few long-lived events.

Routing transients account for 45% of peninsula events.

Abstract

"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.