AP Computer Science

📛 DNS

21 Nov 2016

🎯 AP Learning Targets

I can explain how…

  • The domain name system (DNS) translates domain names to IP addresses.
  • Hierarchy in the DNS helps that system scale.
  • The domain name system (DNS) was not designed to be completely secure.

Build our own DNS

For the next 3 minutes, you will attempt to complete an accurate list matching domain names with IP addresses.

You may only talk to one person at a time.

Discuss

  • Why did I keep taking away your IP addresses?
  • What might be a better system for collecting IP addresses?

DNS (Domain Name Serice)

The service that translates URLs to IP addresses.

Especially in the world of mobile devices it is very common for a device to lose an IP address and need to re-acquire one - entering a tunnel, flying on a plane, even moving from one WiFi hotspot to the next.

It is true that at this point in time it’s less likely that a web site with a registered domain name (like Code.org, google.com, or facebook.com) would rapidly change IP addresses, but the great thing about DNS is that even if they did, that change would be transparent to the public and you won’t have to worry about it. Even so huge operations like Facebook, Twitter, etc. actually serve their sites on many hundreds (or thousands) of computers, all with different IP addresses - DNS helps manage that too, so you can just type Microsoft.com and it direct you to the right place.

As an analogy, think about a time when a friend or family member changed their phone number. That affects everyone who needs to know that number and causes some annoying problems. If we had a system like DNS for phone numbers, you’d never have to concern yourself with anything but remembering the person’s name. Of course, every person on earth would have to have a unique name for this to work, so it’s a bit impractical.

– code.org

Assessment

Questions:

1⃣ A single central register of IP addresses and names (i.e. a DNS-style system) is an efficient means of translating human-readable names to IP addresses. Which of the following is NOT solved by DNS?

a) It’s inefficient to have everyone on the Internet maintain their own list of IP addresses.

b) There are too few IP addresses to meet the current demand.

c) When someone new joins the Internet, they need to inform everyone of their IP address.

d) When an IP address changes, it is impossible to locate a computer until the owner announces the change.

2⃣ Why do computers need to periodically check the DNS for websites you have already visited?

3⃣ Why don’t we need to know the IP addresses for our favorite sites?

Research

“The growing threat of DDoS attacks on DNS”

Lenovo, Google websites hijacked by DNS attacks

DNS Flood DDoS Attack Hit Video Gaming Industry with 90 Million Requests per Second

What We Know About Friday’s Massive East Coast Internet Outage