PowerPoint Presentation

The University of AkronSummit CollegeBusiness Technology Dept.2440: 141Web Site Administration

Domain Name SystemInstructor: Enoch E. Damson

Domain Name System/ServiceThe Domain Name System (DNS) is used to translate host names to IP addresses on the InternetAlso called name resolution or address resolutionCreated in the early 1980sThe first UNIX implementation (Berkeley Internet Name Domain-BIND- server) was created in 1984Whenever a host is added, a configuration file has to be manually changedA host represents a service on a server such as FTP or a Web serverThere can be many hosts on a single computerWindows networks use DNS to resolve computer names on a LANDNS in Windows is designed to be dynamic as computers are added to the network, DNS automatically changesDomain Name System2ClientsOn 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 usedDomain Name System3Structure of the Internet DomainsDNS is organized into a hierarchical structure that defines domainsDNS arranges host names in a hierarchy to make them easier to manage and findThe DNS hierarchical naming system consists of three levels:Root levelTop-level domain (TLD)Second-level domain (SLD)Domain Name System4Domain NamespacesThe root level domain is "."Significant in creating DNS filesTop-level domains identifies the most general part of the domain nameIt identifies the category of the domain nameThe first few original domains were: com, org, edu, gov, mil, and netSecond-level domains are used to identify the individual or company with the domain nameE.g. microsoft.com, uakron.eduA subdomain is a further division of a second-level domainE.g. gozips.uakron.edu Domain Name System5Domain NamespacesSecond-level domains, such as uakron.edu have control over naming within their domainE.g. sub-domains such as www3 and gozips below:www3.uakron.edugozips.uakron.eduA Web server is commonly named wwwA name such as www.uakron.edu is a fully qualified domain name (FQDN)Domain Name System6Host NamesThe first portion of a URL is typically a host nameTypically different from the name of the computerMany hosts can be associated with the same Web serverDomain Name System7ICANN and IANAInternet Corporation for Assigned Names and Numbers (ICANN) is a non-profit organization that coordinates Internet unique identifiershttp://www.icann.org ICANN is funded primarily through fees paid to ICANN by registry operators and registrarsRegistry 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)Registrars are companies (e.g., GoDaddy, Google, Network Solutions) with which consumers register domain namesInternet Assigned Numbers Authority (IANA) a branch of ICANN that is responsible for the global coordination of the DNS Root, IP addressing, and other Internet protocol resourceshttp://www.iana.org Domain Name System8Top-Level DomainsThe first original top-level domains (TLDs) that were available on the Internet included:com commercial domainsorg mostly nonprofit organizationsnet usually ISPs and other network-supported companiesedu educational institutionsgov U.S. federal government organizationsmil U.S. military organizationsin-addr.arpa for reverse lookupshttp://www.iana.org/domains/root/dbDomain Name System9Other Generic Top-Level DomainsICANN later approved other gTLDs in November 2000 below:biz businessesinfo open to anyonename personal registrationspro Licensed professionals, such as doctors, lawyers, etcaero anything related to air transportmuseum Museumscoop cooperative businesses such as credit unionsDomain Name System10Other Generic Top-Level DomainsOther TLDs later approved by ICANN include:travel travel industryjobs the human resource management communitymobi consumers and providers of mobile products and servicesasia Pan-Asia and Asia Pacific regionxxx online adult entertainment (approved in 2011)Source: http://www.pcmag.com/article2/0,2817,2382226,00.asp There were about 22 gTLDs (Generic TLDs)In June 2011, ICANN voted to allow a new array of TLDs at a cost of $185,000 eachSource: http://www.cnn.com/2011/TECH/web/06/20/domain.names.explainer/index.html?hpt=hp_c1Domain Name System11Country Top-Level DomainsThere are about 250 country-specific TLDsSome 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 System12Domain Name RegistrationDomain names are available on a first-come, first-served basisDomain name availability may be verified from locations like:http://www.dslreports.com/whois http://www.instantdomainsearch.comhttp://www.godaddy.comhttp://www.whois.netSome of the things needed include:A valid email addressNames and addresses of the primary and secondary DNS serversA credit card (to pay online)Domain Name System13DNS ComponentsName server also known as DNS serversupports name-to-address and address-to-name resolutionName resolver also called DNS clientCan contact DNS server to lookup nameUsed by browsers, e-mail clients, and client utilities such as pingDomain Name System14DNS ServersThe two main DNS servers that define the Internet are:Primary serversSecondary serversPrimary and secondary servers store the host names used on the InternetThe two main DNS servers that resolve domain names are:Caching serversForwarding serversCaching and forwarding servers search the Internet for host namesDomain Name System15Primary and Secondary ServersPrimary ServerDefines the hosts for the domainMaintains the database for the domainIt has authority for the domainSecondary ServerGets data from primary serverProvides fault tolerance and load distributionRequired for Internet domainsDomain Name System16Primary and Secondary ServersIf you use DNS, you will often work with your ISPIn a simple environment, the ISP will have the primary and secondary DNS serversYou contact them for changesYou can also split the serversISP has primary, you have secondaryYou have primary, ISP has secondaryDomain Name System17Primary and Secondary ServersISPs maintain DNSYou have to send changes to ISPYou have the secondary server which gets updates from the primary serverYour users reference your secondary server which is fasterDomain Name System18Primary and Secondary ServersYou have complete control over DNSYou can make changes whenever you wantIf your primary DNS goes down, the secondary will continue to function (but not indefinitely)Domain Name System19Caching and Forwarding ServersCaching ServerResolves host namesCaches (saves) the resultsAutomatically installed when DNS is installedNo configuration necessaryForwarding ServerCaching server that has access to the Internet and forwards traffic from other caching serversDomain Name System20ZonesA zone is a part of the domain namespaceFor small domains, the domain name represents a single zoneFor large organizations, subdomains can be divided into separately maintained zones Each zone typically has a separate DNSDomain Name System21ZonesZones must be contiguousadmin.uakron.edu can be combined with uakron.eduadmin.uakron.edu cannot be combined with student.uakron.eduThere must be one primary DNS server in each zone (plus a secondary server)Each zone can have multiple secondary DNS serversDomain Name System22Zone File ConfigurationTwo ways of DNS resolutions include:Forward Lookup (resolution)These zones contain entries that map names to IP addressesReverse Lookup (resolution)These zones contain entries that map IP addresses to namesDomain Name System23DNS Configuration in Linux/etc/named.conf describes the files that configure the zonesThere are two primary files that it describesForward lookup is described by named.technowidgets.comIt has the host names and how to handle e-mailReverse lookup is described by named.0.168.192Can be necessary for e-mail (SMTP) and security programsDomain Name System24Starting DNS in LinuxTo start DNS/etc/rc.d/init.d/named startTo restart DNS/etc/rc.d/init.d/named restartTo stop DNS/etc/rc.d/init.d/named stopMake DNS start when you boot LinuxAdd the command to start DNS to /etc/rc.d/rc.localDomain Name System25Configuring Client DNS in LinuxModify /etc/resolv.confThe following line directs the client to use the DNS server at the 192.168.0.100 IP addressnameserver 192.168.0.100The following line associates this computer with the technowidgets.com domaindomain technowidget.comDomain Name System26Testing the DNS in WindowsConfigure a Windows PC to use the DNS server Start->Settings->Network ConnectionsRight-click on Local Area Connection and select PropertiesSelect Internet Protocol (TCP/IP) and click on PropertiesChange DNS to an IP address (to a domain name)Reboot the computer and ping a domain name mapped to the IP address above (such as ping www.uakron.edu)Domain Name System27Name Resolution in WindowsNetBios (computer) names are broadcast to the local networkThe WINS database has computer name to IP address resolutionWindows uses Dynamic DNSDNS is required for Active Directory ServicesDomain Name System28