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1. Ebb and Flow: Implications of ISP Address Dynamics

   Baltra, Guillermo; Song, Xiao; Heidemann, John (March 2024, Proceedings of the Passive and Active Measurement Conference)

   Network traffic is often diurnal, with some networks peaking during the workday and many homes during evening streaming hours. Monitoring systems consider diurnal trends for capacity planning and anomaly detection. In this paper, we reverse this inference and use \emph{diurnal network trends and their absence to infer human activity}. We draw on existing and new ICMP echo-request scans of more than 5.2M /24 IPv4 networks to identify diurnal trends in IP address responsiveness. Some of these networks are \emph{change-sensitive}, with diurnal patterns correlating with human activity. We develop algorithms to clean this data, extract underlying trends from diurnal and weekly fluctuation, and detect changes in that activity. Although firewalls hide many networks, and Network Address Translation often hides human trends, we show about 168k to 330k (3.3--6.4\% of the 5.2M) /24 IPv4 networks are change-sensitive. These blocks are spread globally, representing some of the most active 60\% of \twotwodegree geographic gridcells, regions that include 98.5\% of ping-responsive blocks. Finally, we detect interesting changes in human activity. Reusing existing data allows our new algorithm to identify changes, such as Work-from-Home due to the global reaction to the emergence of Covid-19 in 2020. We also see other changes in human activity, such as national holidays and government-mandated curfews. This ability to detect trends in human activity from the Internet data provides a new ability to understand our world, complementing other sources of public information such as news reports and wastewater virus observation. 

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2. Who Squats IPv4 Addresses?

   https://doi.org/10.1145/3594255.3594260  

   Salamatian, Loqman; Arnold, Todd; Cunha, Ítalo; Zhu, Jiangchen; Zhang, Yunfan; Katz-Bassett, Ethan; Calder, Matt (January 2023, ACM SIGCOMM Computer Communication Review)

   To mitigate IPv4 exhaustion, IPv6 provides expanded address space, and NAT allows a single public IPv4 address to suffice for many devices assigned private IPv4 address space. Even though NAT has greatly extended the shelf-life of IPv4, some networks need more private IPv4 space than what is officially allocated by IANA due to their size and/or network management practices. Some of these networks resort to using squat space , a term the network operations community uses for large public IPv4 address blocks allocated to organizations but historically never announced to the Internet. While squatting of IP addresses is an open secret, it introduces ethical, legal, and technical problems. In this work we examine billions of traceroutes to identify thousands of organizations squatting. We examine how they are using it and what happened when the US Department of Defense suddenly started announcing what had traditionally been squat space. In addition to shining light on a dirty secret of operational practices, our paper shows that squatting distorts common Internet measurement methodologies, which we argue have to be re-examined to account for squat space. 

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3. Durbin: Internet Outage Detection with Adaptive Passive Analysis

   Enayet, Asma; Heidemann, John (November 2024, arxiv)

   Measuring Internet outages is important to allow ISPs to improve their services, users to choose providers by reliability, and governments to understand the reliability of their infrastructure. Today's active outage detection provides good accuracy with tight temporal and spatial precision (around 10 minutes and IPv4 /24 blocks), but cannot see behind firewalls or into IPv6. Systems using passive methods can see behind firewalls, but usually, relax spatial or temporal precision, reporting on whole countries or ASes at 5 minute precision, or /24 IPv4 blocks with 25 minute precision. We propose Durbin, a new approach to passive outage detection that \emph{adapts spatial and temporal precision} to each network they study, thus providing good accuracy and wide coverage with the best possible spatial and temporal precision. Durbin observes data from Internet services or network telescopes. Durbin studies /24 blocks to provide fine spatial precision, and we show it provides good accuracy even for short outages (5 minutes) in 600k blocks with frequent data sources. To retain accuracy for the 400k blocks with less activity, Durbin uses a coarser temporal precision of 25 minutes. Including short outages is important: omitting short outages underestimates overall outage duration by 15\%, because 5\% of all blocks have at least one short outage. Finally, passive data allows Durbin to report this results for outage detection in IPv6 for 15k /48 blocks. Durbin's use of per-block adaptivity is the key to providing good accuracy and broad coverage across a diverse Internet. 

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4. Internet outage detection using passive analysis

   https://doi.org/10.1145/3517745.3563032  

   Enayet, Asma; Heidemann, John (October 2022, Internet Measurements Conference)

   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. 

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5. DynamIPs: analyzing address assignment practices in IPv4 and IPv6

   https://doi.org/10.1145/3386367.3431314  

   Padmanabhan, Ramakrishna; Rula, John P.; Richter, Philipp; Strowes, Stephen D.; Dainotti, Alberto (November 2020, ACM SIGCOMM Conference on emerging Networking EXperiments and Technologies (CoNEXT))

   IP addresses are commonly used to identify hosts or properties of hosts. The address assigned to a host may change, however, and the extent to which these changes occur in time as well as in the address space is currently unknown, especially in IPv6. In this work, we take a first step towards understanding the dynamics of IPv6 address assignments in various networks around the world and how they relate to IPv4 dynamics. We present fine-grained observations of dynamics using data collected from over 3,000 RIPE Atlas probes in dual-stack networks. RIPE Atlas probes in these networks report both their IPv4 and their IPv6 address, allowing us to track changes over time and in the address space. To corroborate and extend our findings, we also use a dataset containing 32.7 billion IPv4 and IPv6 address associations observed by a major CDN. Our investigation of temporal dynamics with these datasets shows that IPv6 assignments have longer durations than IPv4 assignments---often remaining stable for months---thereby allowing the possibility of long-term fingerprinting of IPv6 subscribers. Our analysis of spatial dynamics reveals IPv6 address-assignment patterns that shed light on the size of the address pools network operators use in domestic networks, and provides preliminary results on the size of the prefixes delegated to home networks. Our observations can benefit many applications, including host reputation systems, active probing methods, and mechanisms for privacy preservation. 

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