Behind the Plug

1. Behind the Plug 0010: DNS and tigers and bears, oh my!

2. How’s it Go?

3. The Computer Side HTML Markup (Web Page) Java Applet Flash SWF Web Browser Operating System Processor Memory Monitor Printer … Network Card

4. The Computer Side HTML Markup (Web Page) Java Applet Flash SWF Where does this come from? Web Browser Operating System Processor Memory Monitor Printer … Network Card

5. DNS! • A “web site,” is really just a file sitting on some computer • The “address” you type is something like saying, “get me to Colonial Baptist Church” • It’s not really an “address,” as in relating to a physical location, but a “name” • In fact, it’s called a “domain name” • If you want to find the physical location based on a business name, what do you do? (who’s on first)

6. DNS!

7. DNS! • Where would you go to convert a domain name to an address on the Internet? • A domain name server • …or domain name system server • …or DNS server • Finding the address of a server from its domain name is called resolving the DNS entry • There are three important pieces to DNS • DNS server (or local server, or caching server, or non-authoritative server, or…) • Authoritative server • Root server

8. How DNS Works The web browser asks the DNS server, “what is this server’s address?”

9. How DNS Works This is the address of the DNS server How does your computer know who to ask?

10. How DNS Works So it asks a root server, “where is colonial.org?” DNS Server The DNS server might not know, either… Root Server

11. How DNS Works Authoritative Server It tells the DNS server who the authoritative server is for colonial.org… DNS Server The root server doesn’t know either; it only knows who to ask! Root Server

12. How DNS Works The DNS server then asks the authoritative server, who supplies the answer Authoritative Server DNS Server The DNS server will also “cache” the answer, so if someone else asks within the next few minutes, it will already know the answer

13. How DNS Works And your computer tells your web browser the address of the place you’re trying to go… The DNS server then responds to your computer…

14. How DNS Works • Whew! That’s a lot of work • Why is it this complicated? • The Internet was designed to be resilient • The work is split up among the various people who are paid to do the work • Let’s look at each of these reasons • They are both reasons for a lot of the complexity throughout the Internet, so it’s useful to understand them…

15. Resilience • Resilience is the ability of a system to adapt to changing conditions • A piece of plastic that can bend into all sorts of shapes is “resilient” • A piece of plastic that breaks when you try to bend it is “brittle” • Why is this so important? • The objective of the “original protocol designers” was to build a network that would withstand the results of a nuclear war • In other words, to build a communication system that would survive even if the US were attacked with nuclear weapons

16. Resilience • To make things resilient, break them into smaller pieces • Each piece does a specific job • Each piece can be easily replaced or replicated in a lot of places • It’s like an assembly line • Each piece communicates with every other piece through an API (remember those?)

17. Resilience I can have a lot of authoritative servers —if one breaks, I just use another one… I can have a lot of root servers —if one breaks, I just use another one… I can have a lot of DNS servers —if one breaks, I just use another one… Interchangeable parts!

18. Who Pays? • Who pays to buy all these computers? • Who pays to maintain them? • Who pays to connect them to the Internet? • Who pays to build these databases of names and addresses?

19. Who Pays? • Root Servers • These really just point DNS servers to authoritative servers • The US Government pays for these • Through a contract with a company called ICANN • ICANN contracts Verisign to run and maintain the actual root servers • What the Government won’t pay for is… • To handle individual queries from individual computers all over the Internet • To maintain the database of name to address mappings

20. Who Pays? • Authoritative Servers • These provide the mappings from names to addresses • Content Service Providers pay for these • Such as Inmotion hosting, Myhosting, Big Daddy, Network Solutions, etc. • This is actually bundled into the cost of hosting a web site, or sometimes paid for separately • What they won’t pay for is… • Individual computers asking for information about a specific name to address resolution • The root level servers, because these are shared by everyone in the world

21. Who Pays? • DNS Servers • These accept requests from individual computers connected to the Internet • Access Service Providers pay for these • Time Warner (RoadRunner), AOL, Verizon, etc. • This is actually bundled into your Internet access charge • What they won’t pay for is… • Maintaining the root servers, since these are a globally shared resource • Maintaining the servers that map names to addresses

22. Funny DNS Tricks If you ask for ixquick.com in California, you might get an address in Redmond… If you ask for ixquick.com in Florida, you might get an address in Chicago…

23. Funny DNS Tricks • This is called “geographical DNS” • The idea is to get you to the closest server with the content you want • It improves the speed at which you get the data you’re looking for • It reduces the load on the network by spreading the data around

24. Funny DNS Tricks Did you see it change from pondrings.org to thinkinginchrist.com?

25. Funny DNS Tricks • This is called a domain redirect • When you ask for the address of one server, the DNS server actually gives you the address of another • This is how a lot of “phishing” attacks hide what they’re doing • You ask for “secure.mybank.com,” but the DNS server returns “paswordstealingsite.com”

26. Funny DNS Tricks www.colonial.org student.colonial.org sports.colonial.org The same domain name, but three different servers? What’s going on here?

27. Funny DNS Tricks • These are called subdomains • Each subdomain can actually point to a different server, each with different information on it

28. Looking at DNS

29. Looking at DNS • This is called the “whoisrecord” • You can see… • Who owns a domain • Where they are located • (Sometimes) an email address • (Sometimes) a phone number • (Sometimes) a contact name • This is useful for finding out who runs a web page • Are they trustworthy? • Is this a scam?

30. Looking at DNS • nslookup replicates the query your web browser does when mapping an address to a name • This is sometimes useful… • You can enter the address it returns in your web browser directly

31. Looking at DNS • Speaking of addresses… What is this thing? • It’s an IP address • Technically, it’s an IPv4 address… • This is what we’ll be talking about next time!