What’s the relationship here? DNS  IP addresses What’s the relationship here?

“I don’t use IP addresses!” If IP addresses uniquely identify locations on a network, Why do you not use them when web browsing? What do you use? Ask the students, "If IP addresses uniquely identify locations on a network, why do you not use them when web browsing? What do you use?" As students recall domain names, such as "google.com", ask them, "Why are domain names easier to remember?" "Which has more meaning?" (semantics)

Domain names are mapped to IP addresses by DNS nameservers DNS  IP addresses Domain names are mapped to IP addresses by DNS nameservers (DNS = Domain Name System) DNS nameservers act as ‘address books’ for the Internet

How do DNS nameservers work? Given Domain Name DNS looks up name Finds name! Request routed!  Does not find name Tries another list Repeats with multiple lists until the name is found Name added to local list Repeats query, but name still not found Displays error message (Unable to resolve the server's DNS address.) Walk students through the flowchart. Use the script below to explain it, if necessary. Then ask students to explain it to a neighbor. Explain the following, "Domain names are mapped to IP addresses by DNS nameservers. These nameservers function as 'address books' by doing the following: Given a domain name, they look it up in their current list of names. If it is found, the IP address is resolved and the request may be routed. If it is not found, the nameserver queries another nameserver. Step 2 is repeated until the entry is located or the nameserver has queried a number of prospects, including a root name server (typically a top level server for each of .com, .org, .edu, etc.). If the entry is found, then resolve the request and add the entry to the nameserver's local list for future reference. If the entry is not found, then display an error (e.g., Error 105 (net::ERR_NAME_NOT_RESOLVED): Unable to resolve the server's DNS address.)

Benefits of DNS Semantics! Abstraction encourages other useful features of DNS: What would happen if more than one domain name mapped to a single IP address? In the following scenario, how does the use of domain names differ from that of IP addresses? "An online shopping business in New York has been flooded. They need their web presence to remain online, so they want to relocate their server to the branch office in Scranton, PA." Stress that the benefit in domain names is more than just semantics. Abstraction encourages other useful features of DNS