Understanding Partial Reachability in the Internet Core

Baltra, Guillermo and Saluja, Tarang and Pradkin, Yuri and Heidemann, John
USC/Information Sciences Institute

citation

Guillermo Baltra, Tarang Saluja, Yuri Pradkin and John Heidemann 2026. Understanding Partial Reachability in the Internet Core. ACM New Ideas in Networked Systems (NINeS) (Feb. 2026). [DOI] [PDF]

abstract

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.

reference

@inproceedings{Baltra26a,
  author = {Baltra, Guillermo and Saluja, Tarang and Pradkin, Yuri and Heidemann, John},
  title = {Understanding Partial Reachability in the Internet Core},
  booktitle = { ACM New Ideas in Networked Systems (NINeS)},
  year = {2026},
  sortdate = {2026-02-10},
  project = {ant, eieio, minceq, internetmap, bripod, aquarius},
  month = feb,
  jlocation = {johnh: pafile},
  keywords = {internet definition, islands, peninsulas, partial outages, ripe dnsmon},
  doi = {https://doi.org/10.4230/OASIcs.NINeS.2026.4},
  url = {https://ant.isi.edu/%7ejohnh/PAPERS/Baltra26a.html},
  pdfurl = {https://ant.isi.edu/%7ejohnh/PAPERS/Baltra26a.pdf},
  myorganization = {USC/Information Sciences Institute}
}