Duane Wessels

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.”

A Day at the Root of the Internet

Sebastian Castro, Duane Wessels, Marina Fomenkov, and Kimberly Claffy
Appears in: 
CCR October 2008

We analyzed the largest simultaneous collection of full-payload packet traces from a core component of the global Internet infrastructure ever made available to academic researchers. Our dataset consists of three large samples of global DNS traffic collected during three annual 'Day in the Life of the Internet' (DITL) experiments in January 2006, January 2007, and March 2008.

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