The University of Akron Summit College Business Technology Dept.

1. The University of AkronSummit CollegeBusiness Technology Dept. 2440: 141Web Site Administration Domain Name System Instructor: Enoch E. Damson Domain Name System

2. Domain Name System/Service • The Domain Name System (DNS) is used to translate host names to IP addresses on the Internet • Also called name resolution or address resolution • Created in the early 1980s • The first UNIX implementation (Berkeley Internet Name Domain-BIND- server) was created in 1984 • Whenever a host is added, a configuration file has to be manually changed • A host represents a service on a server such as FTP or a Web server • There can be many hosts on a single computer • Windows networks use DNS to resolve computer names on a LAN • DNS in Windows is designed to be dynamic – as computers are added to the network, DNS automatically changes Domain Name System

3. Clients • On your PC, the TCP/IP configuration contains the address(es) of your DNS server(s) • Whenever you use a URL, whether in a browser, or a utility such as ping, DNS servers are used Domain Name System

4. Structure of the Internet Domains • DNS is organized into a hierarchical structure that defines domains • DNS arranges host names in a hierarchy to make them easier to manage and find • The DNS hierarchical naming system consists of three levels: • Root level • Top-level domain (TLD) • Second-level domain (SLD) Domain Name System

5. Domain Namespaces • The root level domain is "." • Significant in creating DNS files • Top-level domains identifies the most general part of the domain name • It identifies the category of the domain name • The first few original domains were: com, org, edu, gov, mil, and net • Second-level domains are used to identify the individual or company with the domain name • E.g. microsoft.com, uakron.edu • A subdomain is a further division of a second-level domain • E.g. gozips.uakron.edu Domain Name System

6. Domain Namespaces… • Second-level domains, such as uakron.edu have control over naming within their domain • Create hosts such as www, ftp • A name such as www.uakron.edu is a fully qualified domain name (FQDN) • We could create subdomains such as www3 • E.g. www3.uakron.edu Domain Name System

7. Top-Level Domains • A Web server is commonly named www • The original top-level domain (TLD) categories that were available on the Internet included: • com – commercial domains • org – mostly nonprofit organizations • net – usually ISPs and other network-supported companies • edu – educational institutions • gov – U.S. federal government organizations • mil – U.S. military organizations • in-addr.arpa – for reverse lookups • http://www.iana.org/domains/root/db Domain Name System

8. Top-Level Domains… • The Internet Corporation for Assigned Names and Numbers (ICANN) later approved other TLDs below: • biz – businesses • info – open to anyone • name – personal registrations • pro – Licensed professionals, such as doctors, lawyers, etc • aero – anything related to air transport • museum – Museums • coop – cooperative businesses such as credit unions Domain Name System

9. Top-Level Domains… • There are over 200 country-specific domains • Some standard country-specific TLDs include: • .au – Australia • .ca – Canada • .jp – Japan • .sw – Sweden • .uk – United Kingdom • .us – United States (mainly by local and state government agencies and k-12 schools) Domain Name System

10. Domain Name Registration • ICANN (Internet Corporation for Assigned Names and Numbers) is a non-profit organization that coordinates Internet unique identifiers • ICANNis funded primarily through fees paid to ICANN by registrars and registry operators • Registrars are companies (e.g., GoDaddy, Google, Network Solutions) with which consumers register domain names • Registry operators are companies and organizations who operate and administer the master database of all domain names registered in each top level domain (for example VeriSign, Inc. operates .com and .net, Public Interest Registry operates .org, and Neustar, Inc. operates .biz) • http://www.icann.org/en/registrars/accredited-list.html (ICANN accredited Registrars) Domain Name System

11. Domain Name Registration… • Domain names are available on a first-come, first-served basis • The Internet Assigned Numbers Authority (IANA) is responsible for the global coordination of the DNS Root, IP addressing, and other Internet protocol resources • Some of the things needed include: • A non-registered domain name • A valid email address • Names and addresses of the primary and secondary DNS servers • A credit card (to pay online) Domain Name System

12. Host Names • The first portion of a URL is typically a host name • Typically different from the name of the computer • Many hosts can be associated with the same Web server Domain Name System

13. DNS Components • Name server – also known as DNS server • supports name-to-address and address-to-name resolution • Name resolver – also called DNS client • Can contact DNS server to lookup name • Used by browsers, e-mail clients, and client utilities such as ping and tracert Domain Name System

14. DNS Servers that Define the Internet • The two main DNS servers that define the Internet are: • Primary servers • Secondary servers • Primary and secondary servers store the host names used on the Internet • The two main DNS servers that resolve domain names are: • Caching servers • Forwarding servers • Caching and forwarding servers search the Internet for host names Domain Name System

15. Primary and Secondary Servers • Primary Server • Defines the hosts for the domain • Maintains the database for the domain • It has authority for the domain • Secondary Server • Gets data from primary server • Provides fault tolerance and load distribution • Required for Internet domains Domain Name System

16. Primary and Secondary Servers… • If you use DNS, you will often work with your ISP • In a simple environment, the ISP will have the primary and secondary DNS servers • You contact them for changes • You can also split the servers • ISP has primary, you have secondary • You have primary, ISP has secondary Domain Name System

17. Primary and Secondary Servers… • ISPs maintain DNS • You have to send changes to ISP • You have the secondary server which gets updates from the primary server • Your users reference your secondary server which is faster Domain Name System

18. Primary and Secondary Servers… • You have complete control over DNS • You can make changes whenever you want • If your primary DNS goes down, the secondary will continue to function (but not indefinitely) Domain Name System

19. Resolve Host Names • Caching Server • Resolves host names • Caches (saves) the results • Automatically installed when DNS is installed • No configuration necessary • Forwarding Server • Caching server that has access to the Internet and forwards traffic from other caching servers Domain Name System

20. Zones • A zone is a part of the domain namespace • For small domains, the domain name represents a single zone • For large organizations, subdomains can be divided into separately maintained zones • Each zone typically has a separate DNS Domain Name System

21. Zones… • Zones must be contiguous • admin.devry.edu can be combined with devry.edu • admin.devry.edu cannot be combined with student.devry.edu • There must be one primary DNS server in each zone (plus a secondary server) • Each zone can have multiple secondary DNS servers Domain Name System

22. Zone File Configuration • Two ways of DNS resolutions include: • Forward Lookup (resolution) • These zones contain entries that map names to IP addresses • Reverse Lookup (resolution) • These zones contain entries that map IP addresses to names Domain Name System

23. DNS Configuration in Linux • /etc/named.conf describes the files that configure the zones • There are two primary files that it describes • Forward lookup is described by named.technowidgets.com • It has the host names and how to handle e-mail • Reverse lookup is described by named.0.168.192 • Can be necessary for e-mail (SMTP) and security programs Domain Name System

24. Starting DNS in Linux • To start DNS • /etc/rc.d/init.d/named start • To restart DNS • /etc/rc.d/init.d/named restart • To stop DNS • /etc/rc.d/init.d/named stop • Make DNS start when you boot Linux • Add the command to start DNS to /etc/rc.d/rc.local Domain Name System

25. Configuring Client DNS in Linux • Modify /etc/resolv.conf • The following line directs the client to use the DNS server at 192.168.0.100 • nameserver 192.168.0.100 • The following line associates this computer with the technowidgets.com domain • domain uakron.edu Domain Name System

26. Test the DNS • Configure a Windows PC to use the DNS server • Start->Settings->Network Connections • Right-click on Local Area Connection and select Properties • Select Internet Protocol (TCP/IP) and click on Properties • Change DNS to 192.168.0.10 • Reboot and ping www.technowidgets.com Domain Name System

27. Name Resolution in Windows • NetBios (computer) names are broadcast to the local network • The WINS database has computer name to IP address resolution • Windows uses Dynamic DNS • DNS is required for Active Directory Services Domain Name System