1. Intro to Computer Networks DNS (Domain Name System) Bob Bradley The University of Tennessee at Martin

2. Intro to Computer Networks DNS (Domain Name System) The automated system used to translate computer names into equivalent IP addresses. A DNS server responds to a query by looking up the name and returning the address. DNS is a global distributed database. If you tell your web browser to connect to www.utm.edu, the web browser will use the DNS system to convert the host name (www.utm.edu) into an IP address (208.47.4.80)

3. Intro to Computer Networks DNS Converts host names to IP addresses www.utm.edu  208.47.4.80 Also does reverse translation IP  Host Name Also used for E-Mail server lookups Example: mail for anybody@utm.edu goes to mail.utm.edu

4. Intro to Computer Networks The DNS Process Whenever a computer needs to connect to a server (such as the www.yahoo.com web server) it has to look up the server’s IP address using the DNS system. Each computer on the Internet has a list of the IP address of a local DNS server. So when a computer needs to look up an IP address, it asks its local DNS server for it.

5. Intro to Computer Networks Step 1 Step 1: If the PC does not already have the address for www.yahoo.com in its own DNS cache, it asks its local DNS server for the IP address information.

6. Intro to Computer Networks Step 2 Step 2: If the local DNS server does not already have the address for www.yahoo.com in its own DNS cache, it asks the root DNS servers for the IP address of Yahoo’s DNS server.

7. Intro to Computer Networks Step 3 Step 3: The root DNS server returns the IP address of Yahoo’s DNS server to the local DNS server.

8. Intro to Computer Networks Step 4 Step 4: The local DNS server connects to Yahoo’s DNS server and asks for www.yahoo.com’s IP address.

9. Intro to Computer Networks Step 5 Step 5: Yahoo’s DNS server returns the IP address information of www.yahoo.com to the local DNS server.

10. Intro to Computer Networks Step 6 Step 6: The local DNS adds www.yahoo.com’s IP address to its cache and then returns the IP address info to the PC.

11. Intro to Computer Networks Step 7 Step 7: The PC adds the IP address info to its local cache and can then connect to www.yahoo.com using that IP address.

12. Intro to Computer Networks Local DNS Remembers The next time your computer (or another computer on your LAN) needs to look up www.yahoo.com’s address, it will ask the local DNS server again. But this time the local DNS server will have the IP info cached and can return it directly.

13. Intro to Computer Networks