 The topic of this week will be DNS security. The domain name system has been created with the goal of mapping human readable domain names to AP addresses. Nowadays, this is only one of the functionality that DNS provides, but we will refer to this basic one here to recap our DNS work. Let's assume you want to access the web page at www.toptop.example.com. This request will issue a DNS request to your local resolver to retrieve the AP address. The local resolver will typically initiate the name resolution process, which will consist in iteratively contacting DNS servers that are authoritative for the part of DNS information you need. This is done in a hierarchical manner. To start, the local resolver will contact one of the root servers, which will return the address of the name server responsible for the .com zone. The local resolver will then query the .com TLD server, which will respond with the address of the name server responsible for example.com. And finally, the local resolver will ask this name server for the AP address for the domain www.toptop.example.com. If everything works fine, this process will result in the querying host receiving the AP address associated with www.toptop.example.com. The domain name server is therefore built on information and infrastructure. In the next video, we will see examples of attacks to both the information stored in the DNS and DNS infrastructure. DNS is a core service in the Internet. However, given how it works and its complexity, it offers a quite extensive attack surface. For example, many of the middle attacks, cache poisoning attacks and injection of corrupted data in zones are some of the possible attacks. We can qualify those as attacks on the information in DNS. In practice, we have seen that attacks on the DNS information are not the only possible ones. There have been cases in which the infrastructure of the DNS has been attacked by using DDoS attacks for example. Last, there are attacks that do not target the DNS directly but that misuse its functionality. Think for example to a reflection and amplification attacks based on DNS. In this lecture, we will see examples of these three categories of attacks. This week, we will explore the following topics. After this introduction, we will look at some examples of attacks against the DNS system. Cache poisoning attacks are an example of attacks on the DNS information. DDoS attacks against the DNS are instead an example of attacks on the infrastructure. Then, we will investigate how the DNS security extensions, DNSSEC, could be misused for distributed denial service attacks. Finally, we will summarize.