Regensburg, Univ., Diss., 2009.

Univ., Diss., 2009--Frankfurt (Main).

Universiẗat, Diss., 2001--Mainz.

Universiẗat, Diss., 2000--Tübingen.

Techn. University, Diss., 2001--Berlin.

Universiẗat, Diss., 2004--Münster (Westfalen).

Tato prce popisuje nvrh a tvorbu testovac­ho prosted­ pro mÄen­ vkonnosti DNS server nad transportn­mi protokoly TCP a UDP. Obsahuje vsledky vkonnostn­ho mÄen­ t­ rznch implementac­ autoritativn­ch DNS server nad s­ovm provozem sloenm z rznch typ DNS dotaz zaslanch pomoc­ rznch s­ovch a transportn­ch protokol. Je provedeno srovnn­ vkonnosti tÄchto implementac­.

The hierarchal distributed database, Domain Name System (DNS) provides name resolution for network applications, which is vital for the functionality of the Internet. An important part of the system design is to distribute the administration by delegation of domains. To maintain the availability of domains it is important that configuration is accurately per-formed. Zonemaster is a tool used for validating the quality of a DNS delegation by testing of misconfigurations. This thesis evaluates Zonemaster and how it relates to other DNS tools. The evaluation was conducted by identifying and designing configuration errors re-garding DNS delegation. These errors were tested by each tool. Their responses together with the extent of documentation regarding test specification was analyzed. The analyzed data was then divided into three categories: number of implemented tests, detected errors and if the test specification referred to a reliable source. The results showed that Zonemas-ter had all the tests implemented, detected and referred to 91,7% of them. / Den hierarkiska distribuerade databasen, domännamnssystem (DNS) utför namnuppslag-ningar för nätverksapplikationer, vilket är en viktig del för Internets funktionalitet. Dess systemdesign möjliggör distribuerad administration genom delegering av domäner. För att behålla tillgängligheten av domäner är det viktigt att konfigurationen utförs korrekt. Zone-master är ett verktyg som används för att validera kvaliteten av en DNS-delegation genom att identifiera felkonfigureringar. Detta examensarbete utvärderar Zonemaster och dess re-lation till andra DNS-verktyg. Utvärderingen genomfördes genom att identifiera och ut-forma konfigurationsfel avseende DNS-delegering. Dessa fel testades av varje verktyg och deras svar, tillsammans med tillhörande testspecifikation analyserades. Analyserat data de-lades sedan in i tre kategorier: antal genomförda test, upptäckta fel och om testspecifikat-ionerna hänvisade till tillförlitliga källor. Resultaten visade att Zonemaster hade alla tester implementerade samt upptäckte och hänvisade till 91,7% av dem.

Domain Name System (DNS) is virtually the distributed directory of the Internet for obtaining the Internet Protocol (IP) addresses to access web resources. DNS has always been one of the prime targets for cyber attackers either to inundate different types of DNS servers with attack traffic and false records or to exploit the DNS protocol to perform targeted attacks to user machines. DNS amplification or reflection attacks are some of the most fundamental types of DNS specific Denial-of-Service (DoS) attacks. In this type of attack, users are denied service as the server needs to process spoofed DNS query from the attackers and victim machines receive unsolicited DNS response. Software Defined Networking (SDN) and Network Function Virtualization (NFV) are the technological breakthroughs which have brought transformational change in operating and maintaining network services. These have also opened new avenues to deal with those cyber-attacks along with introducing a whole new set of security threats or vulnerabilities that need to be taken care of. In this paper, we propose detection and mitigation strategies to combat DNS amplification or reflection attacks leveraging the functionalities of both SDN and NFV. We reviewed the existing literature of related approaches, incorporated Moving Target Defense (MTD) techniques into the security solutions, discussed the deployment options of vDNS (Virtual DNS) servers, and elaborated on the security issues involved with SDN and NFV. This work could potentially augment the security of the DNS infrastructure while improving the scalability and agility and provide future direction in research and practice.

In our everyday life, turbulence is an omnipresent phenomenon and yet remains poorly understood. Its random and chaotic nature makes it a subject almost impossible to treat from the mathematical point of view and, at present, there is no real prospect of a simple analytic theory. Scientists have therefore regarded the numerical simulation as an alternative to compute the relevant properties of turbulent flows. In this context, our thesis aims at developing and using accurate computational methods, namely pseudo-spectral methods, for studying hydrodynamic (1st part) and magnetohydrodynamic (2nd part) turbulence. In the hydrodynamic part, Chapter I introduces the governing equations of fluid mechanics as well as the main issues related to the numerical study of turbulent flows. In particular, the Direct Numerical Simulations (DNS) of turbulence, in which accurate numerical solutions of the Navier-Stokes equations are obtained, are shown to be limited to moderately turbulent flows. Chapter II introduces the Large Eddy Simulation (LES) technique which aims at simulating highly turbulent flows and which is based on a separation of scales. In practice, it consists of simulating the large - resolved - scales of the flow explicitly while modelling the small - unresolved - scales. Two different approaches for modelling the kinetic energy of the unresolved scales are proposed and their respective advantages and drawbacks are discussed. Chapter III is devoted the study of the mixing-layer using both DNS and LES. It consists of an inhomogeneous turbulent flow which has been studied experimentally and for which well-documented measurements are available. A highly accurate DNS mimicking the same experiment has been produced. It allows to study the inhomogeneity and anisotropy properties of this flow. Also, LES of the same flow, using different models, have been evaluated. In Chapter IV, we explore a pseudo-spectral method to investigate turbulence in a pipe. In this case, the method has to take into account two additional difficulties: i) the presence of the boundary and ii) the axis singularity. We detail how to circumvent these issues. The second part of the thesis is devoted to magnetohydrodynamic (MHD) turbulence. It concerns phenomena where electrically conducting flows interact with electromagnetism and for which governing equations are derived in Chapter V. In Chapter VI, a detailed analysis of the energy transfers between the magnetic and velocity fields is performed thanks to a high resolution database of homogeneous MHD turbulence. It provides some insights to understand the physics of the nonlinear interactions and is also a valuable diagnostic in the framework of LES modelling. Finally, the inhomogeneous configuration studied in Chapter III has been extended to MHD. Several statistics related to the kinetic and magnetic energies are measured and LES of this flow are performed and presented in Chapter VII.