1. UNIT 2 LESSON 10 CS PRINCIPLES

2. UNIT 2 LESSON 10 OBJECTIVES Students will be able to: Describe how a system of DNS servers support IP lookups. Explain that DNS is a hierarchical system that supports growth and change.

3. DNS DNS (Domain Name Server) is a hierarchical system that translates domain names into IP addresses. At the top level of DNS are the root servers, which contain information for domains for such as.com or.org. By accessing the correct root, and looking at each of its branches, it is possible for the DNS to follow the branches down to second level and subdomains to find the appropriate IP address. A single DNS may not know all of the information necessary to find an IP address, but by asking other DNSes, it is able to find that information.

4. DNS The DNS is an open standard protocol, which makes it vulnerable to security issues. These issues include DNS cache poisoning and DDoS attacks, among others. In DNS cache poisoning, DNS servers are given an incorrect IP address, thus routing anyone looking for that information to an incorrect website. DDoS attacks occur when a DNS server is sent too many requests at once and is unable to field all of them. This results in the DNS being unable to serve any request, essentially blocking the DNS from use.

5. UNIT 2 JOURNAL #10 While we can’t actually see what’s going on in the DNS in real life, we can compare it to a system that you’ve seen before: the postal service. How can you relate DNS and the postal service? How do DNS and the postal service function differently?

6. POSSIBLE RESPONSE Scaling of DNS requires system of servers organized in a hierarchy, just like there is a system of post offices and hierarchy (main city post office and local neighborhood post offices). Hierarchy of DNS/IP is analogous to country/state/city/zip/street/direction/number. New URL/IP address pairs are sometimes added, just like new homes and addresses are added and the post office needs to know. IP addresses for web pages sometimes do change, just like people sometimes move. When you move, you send in a change of address card; when a web page's IP address changes, it needs to update its DNS, which then shares the IP change with other DNS servers. If you send mail to someone who has moved, it sometimes comes back undelivered. The Internet cannot have undelivered messages, so the DNS server is queried for the current IP address for EVERY web page you visit.

7. U2L10 ACTIVITY To learn more about DNS you will be reading articles about how it works and some of the vulnerabilities of the system, namely DDoS (Distributed Denial of Service) attacks. You will have 20 minutes to read, then we will perform a jigsaw and you will learn about the other articles from your classmates. What is DDoS?, how to launch, and how to stop Growing threat of DDoS: http://www.information- age.com/technology/security/123459033/growing-threat-ddos-attacks-dnshttp://www.information- age.com/technology/security/123459033/growing-threat-ddos-attacks-dns Details of DDoS attacks: http://www.business2community.com/tech-gadgets/the- details-behind-a-denial-of-service-attack-what-it-is-why-it-matters-and-what-you- can-do-to-stop-it-01241089http://www.business2community.com/tech-gadgets/the- details-behind-a-denial-of-service-attack-what-it-is-why-it-matters-and-what-you- can-do-to-stop-it-01241089 Launching and stopping a DDoS attack: https://blog.cloudflare.com/65gbps-ddos-no- problem/https://blog.cloudflare.com/65gbps-ddos-no- problem/