Lixia Zhang

Adaptive forwarding in named data networking

Cheng Yi, Alexander Afanasyev, Lan Wang, Beichuan Zhang, Lixia Zhang
Appears in: 
CCR July 2012

In Named Data Networking (NDN) architecture, packets carry data names rather than source or destination addresses. This change of paradigm leads to a new data plane: data consumers send out Interest packets, routers forward them and maintain the state of pending Interests, which is used to guide Data packets back to the consumers. NDN routers' forwarding process is able to detect network problems by observing the two-way traffic of Interest and Data packets, and explore multiple alternative paths without loops.

Authority server selection in DNS caching resolvers

Yingdi Yu, Duane Wessels, Matt Larson, Lixia Zhang
Appears in: 
CCR April 2012

Operators of high-profile DNS zones utilize multiple authority servers for performance and robustness. We conducted a series of trace-driven measurements to understand how current caching resolver implementations distribute queries among a set of authority servers. Our results reveal areas for improvement in the ``apparently sound'' server selection schemes used by some popular implementations. In some cases, the selection schemes lead to sub-optimal behavior of caching resolvers, e.g. sending a significant amount of queries to unresponsive servers.

Public Review By: 
Renata Teixeira

This paper examines how the most popular implementations of DNS caching resolvers select the authoritative name server to send a query to. This paper answers three main questions (in the authors' own words): (i) “Does the implementation prefer the fastest server?”; (ii) “What are those defects that make some implementations prefer slower servers?”; and (iii) “Does the implementation detect network changes, especially positive changes, in a timely manner?” The authors answer these questions with controlled experiments. They have built a testbed with a DNS infrastructure and a network emulator. They then emulate DNS queries using traces collected at a resolver in a large ISP. The results reveal four different ways in which current DNS cache implementations can pick a sub-optimal authoritative name server. You should read the paper to find out! This paper asks a precise question of practical value and answers it well. Although there have been anecdotal reports of some of the issues discussed in this paper, these issues have never been studied in such a systematic manner. The main weakness that all three reviewers pointed out was that the problem addressed in this paper is somewhat narrow. All reviewers also recognize that the results have practical implications and that the paper does a good job in the analysis. One reviewer expressed concerns with some of the choices of the emulation environment. In particular, in the experiments, the authors use a high value for the DNS TTL, but in practice some popular services use very low TTLs. This issue is left for future analysis. In general, reviewers were positive about this paper. Some extract from reviews: this paper “contains useful engineering data and analyses for improving future DNS caching resolver implementations”; “this is a subtle but important result”; “This paper is a nice survey of popular DNS implementations and a useful guide for practitioners as well as researchers that work in the areas of service deployment, content distribution and server selection.”

Longitudinal Study of BGP Monitor Session Failures

Pei-chun Cheng, Xin Zhao, Beichuan Zhang, and Lixia Zhang
Appears in: 
CCR April 2010

BGP routing data collected by RouteViews and RIPE RIS have become an essential asset to both the network research and operation communities. However, it has long been speculated that the BGP monitoring sessions between operational routers and the data collectors fail from time to time. Such session failures lead to missing update messages as well as duplicate updates during session re-establishment, making analysis results derived from such data inaccurate.

Public Review By: 
Jitendra Padhye

Many researchers use BGP routing data collected by RouteView and RIPE servers as a starting point for their research. The data is affected by failure of BGP sessions between the operational routers and the data collectors, and hence must be sanitized before being used. This sanitization is often done in an ad-hoc manner by individual researchers to suit their needs.
To remedy this situation, the authors have systematically catalogued the session failures in the RouteView and RIPE data gathered over past eight years. The primary contribution of the paper is the database of these failures, which the authors have made available to the public. Furthermore, the authors plan to keep the failure database updated as new data comes in. This database will be a valuable resource to the researchers working in this area.
The authors also draw some basic conclusion from the failure data they gather. They point out that BGP session resets are quire frequent, although the downtime is often less than 10 minutes. Based on correlation between session failures, they conclude that often it is the collector that is at fault. Unfortunately, they are unable to shed any light on why the collectors fail. Some information in this regard may have been useful to improve to the collector’s performance.
The paper makes one wonder whether the flaws in these data sets may have influenced the conclusions of (many!) research studies based on them. The authors (or others) may want to consider it as part of their future work.

Cyclops: The AS-level Connectivity Observatory

Ying-Ju Chi, Ricardo Oliveira, and Lixia Zhang
Appears in: 
CCR October 2008

In this paper we present Cyclops, a system that collects and displays information of AS-level connectivity extracted from looking glasses, route-servers and BGP tables and updates of hundreds of routers across the Internet. From an operational standpoint, Cyclops provides ISPs a view of how their connectivity is perceived from the outside, enabling a comparison between their observed connectivity and their intended connectivity. ISPs can use the tool to detect and diagnose BGP misconfigurations, route leakages or hijacks based on false AS path.

Public Review By: 
Dmitri Krioukov

Can you hear the shape of the Internet? If not, can you see it? Perhaps you would be better off if you are a cyclops. Focusing your single eye on a single AS, you would be able to get a clear view of the AS Internet structure and dynamics at this AS point ("pupil") surrounded by incident AS links ("iris"). Of course, you can refocus, too, but not too fast, or you will get dizzy.
This is the idea behind the Internet AS topology visualization tool presented in the following paper. The authors call it Cyclops ( They collect AS topology data from a variety of sources (RouteViews, RIPE, route servers, etc.) and provide a per-AS interface to it. The user selects an AS and then can check the connectivity of this AS via either the visualizer or the Web interface showing tables with rows of annotation information per incident AS link. The raw data is also available to use in custom scripts. The AS links are annotated with AS relationships (customer-provider or peerpeer), types of neighboring ASs (Tier-1, large/small ISP, stub, etc.), their degrees, times of their first appearance or disappearance, and other information. Perhaps the most useful feature is that the user can track the changes in the connectivity of a given AS over a specified time period. The paper concludes with some case studies (AS route leakage, outage, and depeerings) that utilize this feature.
Overall, the paper presents a nice interface/visualization tool for Internet AS topology studies that the Internet research community and ISPs may find useful.

Observing the Evolution of Internet AS Topology

Ricardo V. Oliveira, Beichuan Zhang, and Lixia Zhang
Appears in: 
CCR October 2007

Characterizing the evolution of Internet topology is important to our understanding of the Internet architecture and its interplay with technical, economic and social forces. A major challenge in obtaining empirical data on topology evolution is to identify real topology changes from the observed topology changes, since the latter can be due to either topology changes or transient routing dynamics. In this paper, we formulate the topology liveness problem and propose a solution based on the analysis of BGP data.

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