As the backbone of the domain name system (DNS), DNS resolvers are essential to the Internet. Nowadays, the measurement of DNS resolvers, especially open DNS resolvers, has become a research focus. Previous research works show that DNS responses returned from some open DNS resolvers are not expected for clients and the Internet. We call these DNS responses ‘unexpected DNS responses’. Research on unexpected DNS responses is beneficial to the research, usage and management of open DNS resolvers. This paper explores unexpected DNS responses returned from open DNS resolvers in terms of identification and classification to better understand the behaviours of open DNS resolvers. First, an identification method is proposed to identify all kinds of DNS responses from each section of DNS messages. Second, a classification method is proposed to classify unexpected DNS responses by their influences on clients and the Internet. Furthermore, an efficient identification and classification method is proposed to simplify the above process. Among about 9 million responding open DNS resolvers in the experiments on the IPv4 address space, about 40% return unexpected DNS responses. Experimental results show that the proposed methods can identify and classify all kinds of DNS responses returned from open DNS resolvers.

中文翻译：

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开放式 DNS 解析器的非预期 DNS 响应研究

作为域名系统 (DNS) 的骨干，DNS 解析器对 Internet 至关重要。如今，DNS解析器，尤其是开放式DNS解析器的测量已成为研究热点。以前的研究工作表明，客户端和 Internet 不会期望从一些开放的 DNS 解析器返回的 DNS 响应。我们将这些 DNS 响应称为“意外 DNS 响应”。对非预期 DNS 响应的研究有利于开放 DNS 解析器的研究、使用和管理。本文从识别和分类方面探讨了从开放 DNS 解析器返回的意外 DNS 响应，以更好地了解开放 DNS 解析器的行为。首先，提出了一种识别方法，从DNS消息的每个部分中识别出各种DNS响应。第二，提出了一种分类方法，通过对客户端和 Internet 的影响对意外的 DNS 响应进行分类。此外，提出了一种有效的识别和分类方法来简化上述过程。在 IPv4 地址空间的实验中，大约 900 万个响应的开放 DNS 解析器中，大约 40% 返回了意外的 DNS 响应。实验结果表明，所提出的方法可以识别和分类从开放 DNS 解析器返回的各种 DNS 响应。