Application layer Denial-of-Service (DoS) attacks are generated by exploiting vulnerabilities of the protocol implementation or its design. Unlike volumetric DoS attacks, these are stealthy in nature and target a specific application running on the victim. There are several attacks discovered against popular application layer protocols in recent years. In this article, we provide a structured and comprehensive survey of the existing application layer DoS attacks and defense mechanisms. We classify existing attacks and defense mechanisms into different categories, describe their working, and compare them based on relevant parameters. We conclude the article with directions for future research.

中文翻译：

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应用层拒绝服务攻击和防御机制

应用层拒绝服务 (DoS)攻击是通过利用协议实现或其设计的漏洞产生的。与体积 DoS 攻击不同，这些攻击本质上是隐秘的，并且针对在受害者身上运行的特定应用程序。近年来发现了几种针对流行应用层协议的攻击。在本文中，我们对现有的应用层 DoS 攻击和防御机制进行了结构化和全面的调查。我们将现有的攻击和防御机制分为不同的类别，描述它们的工作原理，并根据相关参数进行比较。我们以未来研究的方向结束这篇文章。