This work deals with the security of computer networks based on TCP/IP protocol stack. The main objective is to develop a generator of DoS flooding attacks which carries out attacks such SYN flood, RST flood, UDP flood, ICMP flood, ARP flood, DNS flood and DHCP starvation. The theoretical part describes the features of the mentioned attacks and protocols or mechanisms associated with them. Next part deals with the comparison of selected tools (Hping3, Mausezahn, Trafgen) in terms of number of packets per second (pps) and the link utilization (MB/s). The practical part describes design and implementation of the new attacking tool. There is explained the importance of it’s individual modules, it’s installation and usage options. New tool is also being tested. Then there is described the development, options and installation of control interface which is in the form of web application.

The diploma thesis deals with the problems of DoS/DDoS attacks and development of a tool, in C lanugage, for generating them. In the first chapter the principles of DoS attacks targeting the internet and transport layers of ISO/OSI model are described and also according to their characteristics divided. Selected attacks on the application layer are also described here in detail togehter with protocols which they are based on. In the following chapter there has been created a comparison of freely available tools, which could be used as a attack generators. The practical part is dedicated to a development of a tool for DoS attacks, especially design, general description and usage. Further there is a summary of the newly created library, including results of web server testing, and extensions of a web interface, which is part of the developed tool.