News Archive

CAIDA Examines Severe Network Outages, Offers Prevention Measures

Published November 30, 2023


By Kimberly Mann Bruch, SDSC Communications

In the early hours of Christmas 2020, a bomb set off in the downtown area of Nashville, Tennessee abruptly disrupted AT&T’s regional access network. Not only was this physically devastating to the network – the headquarters were located right next to the bomb – but the damage was also felt throughout the tri-state area of Tennessee, Kentucky and Alabama as the outage caused a disruption in critical infrastructure such as emergency dispatch via 911, hospital networks and credit card processing systems.

Because these types of incidents create massive networking vulnerabilities, researchers from the Center for Applied Internet Data Analysis (CAIDA) at the San Diego Supercomputer Center (SDSC) at UC San Diego undertook a study to analyze the details of such outages and how to prevent them.

The team reviewed catastrophic outages – both unintentional and intentional attacks – based on access network maps to analyze them and then better understand how to mitigate these situations in the future. They presented their work about network disruptions caused by this incident and similar scenarios at the 32nd Annual Usenix Security Symposium in Anaheim, California. Their conference paper discussed several case studies as well as the issues caused by the lack of redundancy in some access networks.

The researchers’ paper, Access Denied: Assessing Physical Risks to Internet Access Networks, explained that “a single fiber cut can take thousands of customers offline” and the provision of redundancy could prevent that. The team said that often, however, the creation of redundancy may be cost-prohibitive.


This illustration from a recently published CAIDA paper shows how a network attacker must disable either redundant power or redundant fiber to induce an overall failure. Credit: CAIDA

“In addition to a ‘hard wire’ redundant network, another solution we proposed in our paper involves backup cellular connectivity to customer premises equipment,” explained Kimberly (kc) Claffy, CAIDA principal investigator and co-author of the study. “These costs would include modem equipment and service plans, but internet service providers would have to provide more transparency about how their wireline access network is used for backhaul in mobile networks.”

While the study focused on the overall topological diversity of regional access networks, the team’s work also included localized failures of specific networks to inform a risk assessment of access network deployments.

Authors on the paper were Alexander Marder, Johns Hopkins University (formerly CAIDA / UC San Diego); Zesen Zhang, UC San Diego; Ricky Mok and Ramakrishna Padmanabhan, CAIDA / UC San Diego; Bradley Huffaker, CAIDA/ UC San Diego; Matthew Luckie, University of Waikato; Alberto Dainotti, Georgia Tech; kc claffy, CAIDA/ UC San Diego; Alex C. Snoeren and Aaron Schulman, UC San Diego.

This work was supported by the National Science Foundation (grant nos. CNS-2105393, CNS-1901517, CNS-2120399, CNS2212241, CNS-1705024, ITE-2226460, OAC-2131987 and OAC-1724853) and DARPA (grant no. CA-HR00112020014).