Domains & Application Layer. Domain Names. Looking up Domain Names. .biz. .com. .info. .net. .org. Human friendly names. Part 2

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1 Domains & Application Layer Domain Names Part 2 Human friendly names Domain Names Looking up Domain Names IP Addresses are not friendly is who will remember this? Fully Qualified Domain Name (FQDN) usually typed in all lowercase though not case sensitive used by websites & Each domain corresponds to an IP address Domain Name System huge database that stores names & IP addresses applications "look up" the IP address this is called DNS Lookup Domain Name Servers house the database 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer Top Level Domains (TLD) Open Top Level Domains Usually the last 3 characters describes the type of domain examples:.edu,.com,.org Controlled by ICANN: Internet Corporation for Assigned Names and Numbers contracted with the U.S. new ones are being created.biz.com.info.net.org Commercial Business Commercial Business Information Network - Open Non-Profit Organization 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer

2 Restricted Top Level Domains World State Top Level Domains.edu Educational Institutions.ca Canada.gov United States Government.cn China.int International Organizations.br Brazil.mil United States Military.gr Greece.pro Licensed Professionals.in India 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer World State Top Level Domains World State Top Level Domains.ie Ireland.il Israel.eu European Union.jp Japan.kr South Korea.ly Libya.pk Pakistan.ru Russia.se Sweden.uk Britain (United Kingdom) 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer ICANN Now Allows Custom TLDs! Once Proposed Top Level Domains There was a huge a debate over adding new TLDs Good domains were running out, so it seemed like a good idea to expand.kids.mail.geo.post.xxx Kid-friendly websites SPAM-free Mail Geographic Locations Post Office (restricted) Take a wild guess! 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer

3 ICANN Now Allows Custom TLDs! On July 24, 2008, ICANN... voted to allow any top level domain bought like regular domains.com,.org, etc... are public New TLDs can act as a hub Apple could get.mac mail.mac, store.mac, etc... Facebook could get.facebook Went live in Summer 2013 How Domain Names Work Behind the scenes, but very important 6/11/2018 Sacramento State - Cook - CSc 8 - Summer Domain Name System The Top-Level Domain Servers Distributed database implemented in hierarchy of many name servers Why not centralized? single point of failure traffic volume would be too high maintenance doesn t scale! 6/11/2018 Sacramento State - Cook - CSc 8 - Summer Information about different top-level domains is given to different servers around the World TLDs include: public use:.com,.org,.net, etc restricted:.edu,.gov, etc all top-level country domains:.uk,.fr,.ca,.jp 6/11/2018 Sacramento State - Cook - CSc 8 - Summer The Top-Level Domain Servers DNS Servers around the World There are 13 top-level servers World-Wide each is assigned a letter such as A, B, C, originally the servers had more personalized names like Internic.net, but they were changed for consistency Locations some are solely found in one country but others distribute their servers using anycast technology 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer

4 Authoritative Servers Local Name Server Authoritative DNS servers hold the actual, official, domain/ip mappings DNS requests are sent to these servers There are over 200 servers in the World about 100 in the United States Non-authoritative DNS servers are other servers that "remember" what a domain's IP address is often they will respond with an answer 6/11/2018 Sacramento State - Cook - CSc 8 - Summer Sometimes a domain will create subdomains for its services For example: csus.edu has a sub-domain called saclink.csus.edu Does this get entered into the main DNS databases? 6/11/2018 Sacramento State - Cook - CSc 8 - Summer Local Name Server Example: Connect to athena.csus.edu No it's maintained by a It is also called a default name server maintains a lookup table for all local computers for instance, "csus.edu" handles all "«sub domain».csus.edu" requests itself When a host makes a query, it is sent to its and then bubbles up until some server has an answer dns.csus.edu athena.csus.edu? athena.csus.edu IP athena.csus.edu IP dns.comcast.com athena? csus.edu IP.edu server.edu?.edu server IP csus.edu? Root server 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer Example: FQDN Is Cached Looking up Domain Names dns.csus.edu athena.csus.edu? athena.csus.edu IP dns.comcast.com.edu server Root server UNIX/Linux and Windows have a tool called nslookup that can look up a domain This tool can lookup any Fully Qualified Domain Name (FQDN) For example: saclink.csus.edu edu is the top level domain csus is a subdomain saclink is the name of a host 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer

5 nslookup Example nslookup Example 2 C:\Users\Devin>nslookup gaia.csus.edu Server: ns4.csus.edu Address: Name: gaia.ecs.csus.edu Address: Aliases: gaia.csus.edu Local server ns4 responded C:\Users\Devin>nslookup flowgorithm.org Server: cdns01.comcast.net Address: 2001:558:feed::1 Non-authoritative answer: Name: flowgorithm.org Address: name server responded, but is local, not authoritative 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer Internet Protocols Internet Application Layer Application Layer Transport Layer Network Layer Any Data Internet TCP / IP Common Application Layer Protocols Data link Layer Physical Layer 6/11/2018 Sacramento State - Cook - CSc 8 - Summer Application Layer Protocols Hypertext Transfer Protocol HTTP Hyper Text Transfer Protocol FTP File Transfer Protocol POP Post Office Protocol SMTP Simple Mail Transfer Protocol Telnet remote computer access SSL Secure Socket Layer Used to transfer webpages each page item is requested separately example: images are loaded at different times HTTP is a stateless protocol one request and response per session login information & state data are not stored cookies are used to store this information 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer

6 Some Common HTTP Codes File Transfer Protocol Code Meaning 200 Okay everything worked 301 Moved Permanently 302 Currently not available 404 Not found resource does not exist 500 Server Error File Transfer Protocol (FTP) Copies files over a network Can copy files to and from another computer Security requires you to log into a site prevents unauthorized access 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer Protocols Telnet SMTP Simple Mail Transfer Protocol used to send like dropping a letter in a mailbox POP Post Office Protocol used to retrieve like picking up a letter from the post office 6/11/2018 Sacramento State - Cook - CSc 8 - Summer Allows the user to connect to a computer remotely Sends / retrieves commands remotely control a computers uses a text-based interface Commonly used by computer scientists 6/11/2018 Sacramento State - Cook - CSc 8 - Summer Servers and Ports and daemons oh my! Programs that provide a service, are called Servers We use the term synonymously with computers designed to provide services, which gets confusing 6/11/2018 Sacramento State - Cook - CSc 8 - Summer

7 It is important to understand how this works Each service represents a different type of connection between two computers Each service uses a different port It is similar to the concept of the physical ports on your computer USB, etc It is a software port only exists in software 16-bit number total of ports built into TCP so it is part of the Internet 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer Software, on the server computer, that listens to on a port is called a daemon When it receives data, it contacts the appropriate software Usually, the name of the daemon is the protocol name + "d" Examples: ftpd daemon for FTP httpd daemon for HTTP 6/11/2018 Sacramento State - Cook - CSc 8 - Summer /11/2018 Sacramento State - Cook - CSc 8 - Summer Some Common Internet Ports Port Name Notes 20 FTP Data Data for File Transfer Protocol 21 FTP Control Control commands for FTP 25 SMTP Simple Mail Transfer Protocol 54 DNS Domain Name Service 80 HTTP Hypertext Transfer Protocol 110 POP3 Post Office Protocol 443 HTTPS Secure HTTP 6/11/2018 Sacramento State - Cook - CSc 8 - Summer