DNS Internet Papers Publications Uncategorized

new paper “Defending Root DNS Servers Against DDoS Using Layered Defenses” at COMSNETS 2023 (best paper!)

Our paper titled “Defending Root DNS Servers Against DDoS Using Layered Defenses” will appear at COMSNETS 2023 in January 2023. In this work, by ASM Rizvi, Jelena Mirkovic, John Heidemann, Wes Hardaker, and Robert Story, we design an automated system named DDIDD with multiple filters to handle an ongoing DDoS attack on a DNS root server. We evaluated ten real-world attack events on B-root and showed DDIDD could successfully mitigate these attack events. We released the datasets for these attack events on our dataset webpage (dataset names starting with B_Root_Anomaly).

Update in January: we are happy to announce that this paper was awarded Best Paper for COMSNETS 2023! Thanks for the recognition.

Table II from [Rizvi23a] shows the performance of each individual filter, with near-best results in bold. This table shows that one filter covers all cases, but together in DDIDD they provide very tood defense.

From the abstract:

Distributed Denial-of-Service (DDoS) attacks exhaust resources, leaving a server unavailable to legitimate clients. The Domain Name System (DNS) is a frequent target of DDoS attacks. Since DNS is a critical infrastructure service, protecting it from DoS is imperative. Many prior approaches have focused on specific filters or anti-spoofing techniques to protect generic services. DNS root nameservers are more challenging to protect, since they use fixed IP addresses, serve very diverse clients and requests, receive predominantly UDP traffic that can be spoofed, and must guarantee high quality of service. In this paper we propose a layered DDoS defense for DNS root nameservers. Our defense uses a library of defensive filters, which can be optimized for different attack types, with different levels of selectivity. We further propose a method that automatically and continuously evaluates and selects the best combination of filters throughout the attack. We show that this layered defense approach provides exceptional protection against all attack types using traces of real attacks from a DNS root nameserver. Our automated system can select the best defense within seconds and quickly reduce the traffic to the server within a manageable range while keeping collateral damage lower than 2%. We can handle millions of filtering rules without noticeable operational overhead.

This work is partially supported by the National Science
Foundation (grant NSF OAC-1739034) and DHS HSARPA
Cyber Security Division (grant SHQDC-17-R-B0004-TTA.02-
0006-I), in collaboration with NWO.

A screen capture of the presentation of the best paper award.

Outages Presentations Publications Uncategorized

new poster “Internet Outage Detection Using Passive Analysis” at ACM IMC 2022

Asma Enayet will present her poster “Internet Outage Detection Using Passive Analysis” by Asma Enayet and John Heidemann at ACM Internet Measurement Conference, Nice, France from October 25-27th, 2022.

We expect the ACM poster abstract (without the poster) to appear at in October 2022.

We are making a report available now with the poster abstract and poster at as a pre-print.

From the abstract:

Outages from natural disasters, political events, software or hardware issues, and human error place a huge cost on e-commerce ($66k per minute at Amazon). While several existing systems detect Internet outages, these systems are often too inflexible, with fixed parameters across the whole internet with CUSUM-like change detection. We instead propose a system using passive data, to cover both IPv4 and IPv6, customizing parameters for each block to optimize the performance of our Bayesian inference model. Our poster describes our three contributions: First, we show how customizing parameters allows us often to detect outages that are at both fine timescales (5 minutes) and fine spatial resolutions (/24 IPv4 and /48 IPv6 blocks). Our second contribution is to show that, by tuning parameters differently for different blocks, we can scale back temporal precision to cover more challenging blocks. Finally, we show our approach extends to IPv6 and provides the first reports of IPv6 outages.

IPv6 Coverage: our source of passive data (B-Root) is incomplete, but it provides similar coverage in both IPv4 and IPv6.
IPv6 Outages: Outage rate for IPv6 (12%) is greater than for IPv4 (5.5%) —IPv6 reliability can improve.

This work was supported by NSF grant CNS-2007106 (EIEIO).

Internet Papers Publications Software releases

new paper “Chhoyhopper: A Moving Target Defense with IPv6” at NDSS MADWeb Workshop 2022

On April 24, 2022 we will publish a new paper titled “Chhoyhopper: A Moving Target Defense with IPv6” by A S M Rizvi and John Heidemann at the 4th Workshop on Measurements, Attacks, and Defenses for the Web (MADWeb 2022), co-located with NDSS. We provide Chhoyhopper as an open-source tool for SSH and HTTPS—try it out!

From the abstract:

Services on the public Internet are frequently scanned, then subject to brute-force password attempts and Denial-of-Service (DoS) attacks. We would like to run such services stealthily, where they are available to friends but hidden from adversaries. In this work, we propose a discovery-resistant moving target defense named “Chhoyhopper” that utilizes the vast IPv6 address space to conceal publicly available services. The client meets the server at an IPv6 address that changes in a pattern based on a shared, pre-distributed secret and the time of day. By hopping over a /64 prefix, services cannot be found by active scanners, and passively observed information is useless after two minutes. We demonstrate our system with the two important applications—SSH and HTTPS, and make our system publicly available.

Client and server interaction in Chhoyhopper. A Client with the right secret key can only get access into the system.

Thanks: A S M Rizvi and John Heidemann’s work on this paper is supported, in part, by the DHS HSARPA Cyber Security Division via contract number HSHQDC-17-R-B0004-TTA.02-0006-I (PAADDoS), and by DARPA under Contract No. HR001120C0157 (SABRES). Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of NSF or DARPA. We thank Rayner Pais who prototyped an early version of Chhoyhopper and version in IPv4 hopping over ports.

Anycast BGP Internet

new paper “Anycast Agility: Network Playbooks to Fight DDoS” at USENIX Security Symposium 2022

We will publish a new paper titled “Anycast Agility: Network Playbooks to Fight DDoS” by A S M Rizvi (USC/ISI), Leandro Bertholdo (University of Twente), João Ceron (SIDN Labs), and John Heidemann (USC/ISI) at the 31st USENIX Security Symposium in Aug. 2022.

A sample anycast playbook for a 3-site anycast deployment. Different routing configurations provide different traffic mixes. From [Rizvi22a, Table 5].

From the abstract:

IP anycast is used for services such as DNS and Content Delivery Networks (CDN) to provide the capacity to handle Distributed Denial-of-Service (DDoS) attacks. During a DDoS attack service operators redistribute traffic between anycast sites to take advantage of sites with unused or greater capacity. Depending on site traffic and attack size, operators may instead concentrate attackers in a few sites to preserve operation in others. Operators use these actions during attacks, but how to do so has not been described systematically or publicly. This paper describes several methods to use BGP to shift traffic when under DDoS, and shows that a response playbook can provide a menu of responses that are options during an attack. To choose an appropriate response from this playbook, we also describe a new method to estimate true attack size, even though the operator’s view during the attack is incomplete. Finally, operator choices are constrained by distributed routing policies, and not all are helpful. We explore how specific anycast deployment can constrain options in this playbook, and are the first to measure how generally applicable they are across multiple anycast networks.

Dataset used in this paper are listed at, and the software used in our work is at They are provided as part of Call for Artifacts.

Acknowledgments: A S M Rizvi and John Heidemann’s work on this paper is supported, in part, by the DHS HSARPA Cyber Security Division via contract number HSHQDC-17-R-B0004-TTA.02-0006-I. Joao Ceron and Leandro Bertholdo’s work on this paper is supported by Netherlands Organisation for scientific research (4019020199), and European Union’s Horizon 2020 research and innovation program (830927). We would like to thank our anonymous reviewers for their valuable feedback. We are also grateful to the Peering and Tangled admins who allowed us to run measurements. We thank Dutch National Scrubbing Center for sharing DDoS data with us. We also thank Yuri Pradkin for his help to release our datasets.

DNS Papers Publications

New paper and talk “Institutional Privacy Risks in Sharing DNS Data” at Applied Networking Research Workshop 2021

Basileal Imana presented the paper “Institutional Privacy Risks in Sharing DNS Data” by Basileal Imana, Aleksandra Korolova and John Heidemann at Applied Networking Research Workshop held virtually from July 26-28th, 2021.

From the abstract:

We document institutional privacy as a new risk
posed by DNS data collected at authoritative servers, even
after caching and aggregation by DNS recursives. We are the
first to demonstrate this risk by looking at leaks of e-mail
exchanges which show communications patterns, and leaks
from accessing sensitive websites, both of which can harm an
institution’s public image. We define a methodology to identify queries from institutions and identify leaks. We show the
current practices of prefix-preserving anonymization of IP
addresses and aggregation above the recursive are not sufficient to protect institutional privacy, suggesting the need for
novel approaches.

Number of MX and DNSBL queries in a week-long root DNS data that can potentially leak email-related activity

The data from this paper is available upon request, please see our project page.

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