(There have been many articles about DOS (DenialofService, that is, denial of service) attacks, but most people still don't know what DOS is and how it is implemented. This article mainly introduces the mechanism and common implementation methods of DOS. Because I have carefully understood the TCP/IP protocol and RFC documents some time ago, I have a little experience. At the same time, some of the content in the article is translated from Shaft's article. To understand the realization mechanism of DOS attack, you must have a certain understanding of TCP.)