Hello and welcome to this section of the course focusing on the third and final service, AWS Shield. AWS Shield is closely related to both AWS WAF and also the AWS Firewall Manager. So what is it used for? Well, AWS Shield has been designed to help protect your infrastructure against distributed denial of service attacks, commonly known as DDoS. These attacks are very common, and the attack itself targets a host which might be running a website or web application, and it receives a huge number of requests simultaneously sent maliciously by an attacker from multiple distributed sources. This increase and flood of traffic aims to prevent legitimate requests getting through to host and being processed, while at the same time severely hindering the performance of the application or website. So much so in fact, that users often think the site is down. 

There are a number of different types of DDoS takes that can take place, for example, a SYN Flood. In a Syn Flood attack, a large number of connections are made to the host under attack. The host will then respond accordingly with an SYN/ACK packet, at which point the client sending the original connection request would normally respond with another SYN, completing the three-way handshake to allow communications to begin. However, this final SYN packet is not sent to the host, and this leaves a huge number of open connections on the host, resulting in diminished resources available to process legitimate requests. DNS Query Flood. By using multiple DNS queries an attacker can drain the resources against a DNS server, such as Route 53 in AWS. HTTP flood and cache-busting attacks. These attacks operate at layer seven, the application layer. And during an HTTP flood attack an attacker sends a large amount of HTTP requests, which may include POST and GET requests to a host, consuming the resources available. Cache-busting attacks are similar to HTTP floods, however, by using the HTTP request query string they are able to force content to be retrieved from the originating server, rather than from an edge location, which impacts the performance of the source servers available resources unnecessarily. AWS Shield itself is available at two different levels of features, AWS Shield Standard and AWS Shield Advanced, and AWS shield advanced has a lot more power and protection on offer than standard. AWS Shield Standard is free to everyone, well, at least anyone who has an AWS account, and it offers DDoS protection against some of the more common layer three, the network layer, and layer four, transport layer, DDoS attacks. This protection is integrated with both CloudFront and Route 53. 

AWS Shield advanced offers a greater level of protection for DDoS attacks across a wider scope of AWS services for an additional cost. This advanced level offers protection against your web applications running on EC2, CloudFront, ELB and also Route 53. In addition to these additional resource types being protected, there are enhanced levels of DDoS protection offered compared to that of Standard. And you will also have access to a 24-by-seven specialized DDoS response team at AWS, known as DRT. With these additional features, the advanced level also provides an enhanced monitoring capability allowing you to view real-time metrics of any attacks against your resources. Whereas the Standard version of Shield offered protection against layer three and layer four, Advanced also offers protection against layer seven, application, attacks. Another great advantage is the fact that you also get cost protection as a part of the plan, whereby your resources may scale suddenly and unexpectedly to cope with the rise in traffic. From a cost perspective, if your decide to go with AWS Shield Advanced then you also get AWS WAF included in the same price, and this price is currently $3,000 a month, plus data transfer fees. As you can see from this image, there are a significant amount of advantages with the Advanced version of AWS Shield over Standard. That now brings me to the end of this lecture. Coming up next I shall provide an overview of how to set up and implement AWS Shield Advanced.