Internet Outages

Observing the CenturyLink outage on 2020-08-30

CenturyLink / Level3 was reported to have a major outage on Sunday, 2020-08-30 (as reported on CNN and discussed on slashdot).

This outage was very clear in our Trinocular near-real-time outage detection system. We have summarized the details with images, before, during, and after, and an animation of the nearly 7-hour event or see the event on our near-real-time outage website.

This outage is one of the largest U.S. nation-wide events since the 2014-08-27 Time Warner outage.

DNS Internet

APNIC Blog Post on the effects of chromium generated DNS traffic to the root server system

During the summer of 2019, Haoyu Jiang and Wes Hardaker studied the effects of DNS traffic sent to the root serevr system by chromium-based web browsers. The results of this short research effort were posted to the APNIC blog.

DNS Internet

B-root’s new sites reduce latency

B-Root, one of the 13 root DNS servers, deployed three new sites in January 2020, doubling its footprint and adding its first sites in Asia and Europe. How did this growth lower latency to users? We looked at B-Root deployment with Verfploter to answer this question. The end result was that new sites in Asia and Europe allowed users there to resolve DNS names with B-Root with lower latency (see the catchment map below). For more details please review our anycast catchment page.

B-root added 3 new sites in Singapore, Washington, DC, and Amsterdam to their three existing 3 sites in Los Angeles, Chile, and Miami. The graph below shows anycast catchments after these sites were deployed (each color in the pie charts shows traffic to a different site).

Announcements DNS Internet

Early longitudinal results in measuring the usage of Mozilla’s DNS Canary

Mozilla announced the creation of a “” “Canary Domain” that could be configured within ISPs to disable Firefox’s default use of DNS over HTTPS. On 2019/09/21 Wes Hardaker created a RIPE Atlas measurement to study resolvers within ISPs that had been configured to return an NXDOMAIN response. This measurement is configured to have 1000 Atlas probes query for the name once a day.

The full description of methodology is on Wes’ ISI site, which should receive regular updates to the graph.


DNS Papers Publications

new conference paper “When the Dike Breaks: Dissecting DNS Defenses During DDoS” at ACM IMC 2018

We have published a new paper “When the Dike Breaks: Dissecting DNS Defenses During DDoS” in the ACM Internet Measurements Conference (IMC 2018) in Boston, Mass., USA.

From the abstract:

Caching and retries protect half of clients even with 90% loss and an attack twice the cache duration. (Figure 7c from [Moura18b].)

The Internet’s Domain Name System (DNS) is a frequent target of Distributed Denial-of-Service (DDoS) attacks, but such attacks have had very different outcomes—some attacks have disabled major public websites, while the external effects of other attacks have been minimal. While on one hand the DNS protocol is relatively simple, the \emph{system} has many moving parts, with multiple levels of caching and retries and replicated servers. This paper uses controlled experiments to examine how these mechanisms affect DNS resilience and latency, exploring both the client side’s DNS \emph{user experience}, and server-side traffic. We find that, for about 30\% of clients, caching is not effective. However, when caches are full they allow about half of clients to ride out server outages that last less than cache lifetimes, Caching and retries together allow up to half of the clients to tolerate DDoS attacks longer than cache lifetimes, with 90\% query loss, and almost all clients to tolerate attacks resulting in 50\% packet loss. While clients may get service during an attack, tail-latency increases for clients. For servers, retries during DDoS attacks increase normal traffic up to $8\times$. Our findings about caching and retries help explain why users see service outages from some real-world DDoS events, but minimal visible effects from others.

Datasets from this paper are available at no cost and are listed at


DNS Papers Presentations Publications

New paper and talk “Enumerating Privacy Leaks in DNS Data Collected above the Recursive” at NDSS DNS Privacy Workshop 2018

Basileal Imana presented the paper “Enumerating Privacy Leaks in DNS Data Collected  above the Recursive” at NDSS DNS Privacy Workshop in San Diego, California, USA on February 18, 2018. Talk slides are available at and paper is available at, or can be found at the DNS privacy workshop page.

From the abstract:

Threat model for enumerating leaks above the recursive (left). Percentage of four categories of queries containing IPv4 addresses in their QNAMEs. (right)

As with any information system consisting of data derived from people’s actions, DNS data is vulnerable to privacy risks. In DNS, users make queries through recursive resolvers to authoritative servers. Data collected below (or in) the recursive resolver directly exposes users, so most prior DNS data sharing focuses on queries above the recursive resolver. Data collected above a recursive resolver has largely been seen as posing a minimal privacy risk since recursive resolvers typically aggregate traffic for many users, thereby hiding their identity and mixing their traffic. Although this assumption is widely made, to our knowledge it has not been verified. In this paper we re-examine this assumption for DNS traffic above the recursive resolver. First, we show that two kinds of information appear in query names above the recursive resolver: IP addresses and sensitive domain names, such as those pertaining to health, politics, or personal or lifestyle information. Second, we examine how often these classes of potentially sensitive names appear in Root DNS traffic, using 48 hours of B-Root data from April 2017.

This is a joint work by Basileal Imana (USC), Aleksandra Korolova (USC) and John Heidemann (USC/ISI).

The DITL dataset (ITL_B_Root-20170411) used in this work is available from DHS IMPACT, the ANT project, and through DNS-OARC.

Announcements Outages

new website for browsing Internet outages

We are happy to announce a new website at that supports our Internet outage data collected from Trinocular.

The ANT Outage world browser, showing Hurricane Irma just after landfall in Florida in Sept. 2017.

Our website supports browsing more than two years of outage data, organized by geography and time.  The map is a google-maps-style world map, with circle on it at even intervals (every 0.5 to 2 degrees of latitude and longitude, depending on the zoom level).  Circle sizes show how many /24 network blocks are out in that location, while circle colors show the percentage of outages, from blue (only a few percent) to red (approaching 100%).

We hope that this website makes our outage data more accessible to researchers and the public.

The raw data underlying this website is available on request, see our outage dataset webpage.

The research is funded by the Department of Homeland Security (DHS) Cyber Security Division (through the LACREND and Retro-Future Bridge and Outages projects) and Michael Keston, a real estate entrepreneur and philanthropist (through the Michael Keston Endowment).  Michael Keston helped support this the initial version of this website, and DHS has supported our outage data collection and algorithm development.

The website was developed by Dominik Staros, ISI web developer and owner of Imagine Web Consulting, based on data collected by ISI researcher Yuri Pradkin. It builds on prior work by Pradkin, Heidemann and USC’s Lin Quan in ISI’s Analysis of Network Traffic Lab.

ISI has featured our new website on the ISI news page.


DNS Presentations

new talk “LocalRoot: Serve Yourself”

Wes Hardaker gave a talk on his LocalRoot project, allowing recursive resolver operators to keep an up to date cached copy of the root zone data available at all times. The talk was held in Abu Dhabi on November 1, 2017 at the ICANN annual general meeting during the DNSSEC Workshop. Slides and recorded video are available at on the ICANN event page.

DNS Papers Publications

new journal paper “Detecting Malicious Activity With DNS Backscatter Over Time” in IEEE/ACM ToN Oct, 2017

The paper “Detecting Malicious Activity With DNS Backscatter Over Time ” appears in EEE/ACM  Transactions on Networking ( Volume: 25, Issue: 5, Oct. 2017 ).

From the abstract:

Network-wide activity is when one computer (the originator) touches many others (the targets). Motives for activity may be benign (mailing lists, CDNs, and research scanning), malicious (spammers and scanners for security vulnerabilities), or perhaps indeterminate (ad trackers). Knowledge of malicious activity may help anticipate attacks, and understanding benign activity may set a baseline or characterize growth. This paper identifies DNS backscatter as a new source of information about network-wide activity. Backscatter is the reverse DNS queries caused when targets or middleboxes automatically look up the domain name of the originator. Queries are visible to the authoritative DNS servers that handle reverse DNS. While the fraction of backscatter they see depends on the server’s location in the DNS hierarchy, we show that activity that touches many targets appear even in sampled observations. We use information about the queriers to classify originator activity using machine learning. Our algorithm has reasonable accuracy and precision (70–80%) as shown by data from three different organizations operating DNS servers at the root or country-level. Using this technique we examine nine months of activity from one authority to identify trends in scanning, identifying bursts corresponding to Heartbleed and broad and continuous scanning of ssh.

This paper furthers our understanding of evolution of malicious network activities from an earlier work that:
(1) Why our machine-learning based classifier (that relies on manually collected labeled data) does not port across physical sites and over time.
(2) Secondly paper recommends how to sustain good learning score over time and provides expected life-time of labeled data.

An excerpt from section III-E (Training Over Time):

Classification (§ III-D) is based on training, yet training accuracy is affected by the evolution of activity—specific examples come and go, and the behavior in each class evolves. Change happens for all classes, but the problem is particularly acute for malicious classes (such as spam) where the adversarial nature of the action forces rapid evolution (see § V).


Some datasets used in this paper can be found here:

In-the-news Internet Outages

Evaluation of Hurricane Harvey’s Effects on the Internet’s Edge

On August 25, 2017 Hurricane Harvey made landfall in south Texas, causing widespread property damage, displacing more than 30,000 people, and costing more than 45 lives (as of 2017-09-01).

We sympathize with those were hurt by this disaster, and hope for swift recovery for the region.

We recently examined the effects of Hurricane Harvey on the area using Trinocular, our internet outage detection system.  Two key results:

Trinocular report on outages in Texas after Hurricane Harvey (on 2017-08-28t03:32Z)

We see that landfall was followed by widespread Internet outages in the Corpus Christi area, with 40% or more home networks dropping off the Internet.

We see that over the following days, network outages grew in the Houston area, with many networks dropping off the Internet. However, the fraction of networks lost in Houston was much smaller than in the Corpus Christi area.

More details are on our Hurricane Harvey web page.  We will update that page as we get more data in.

The dataset including Hurricane Harvey will be internet_outage_adaptive_a29all-20170702 and will be released in October 2017. Until the full data is released, we have a preliminary dataset through August 2017 available on request.