The University of AkronSummit College

Business Technology Dept.2440: 141

Web 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 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

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ClientsOn 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

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Structure 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)

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Domain NamespacesThe root level domain is "."

Significant in creating DNS filesTop-level domains identifies the most general part of the

domain name It identifies the category of the domain nameThe 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 nameE.g. microsoft.com, uakron.eduA subdomain is a further division of a second-level domain

E.g. gozips.uakron.edu

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Domain Namespaces…Second-level domains, such as uakron.edu have

control over naming within their domainE.g. sub-domains such as www3 and gozips below:

www3.uakron.edu gozips.uakron.edu

A Web server is commonly named wwwA name such as www.uakron.edu is a fully qualified

domain name (FQDN)

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Host 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

server

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ICANN 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 registrars 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)

Registrars are companies (e.g., GoDaddy, Google, Network Solutions) with which consumers register domain names

Internet 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

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Top-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 organizations in-addr.arpa – for reverse lookups

http://www.iana.org/domains/root/db

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Other Generic Top-Level DomainsICANN later approved other gTLDs in November 2000 below:

biz – businesses info – open to anyonename – personal registrationspro – Licensed professionals, such as doctors, lawyers, etcaero – anything related to air transportmuseum – Museumscoop – cooperative businesses such as credit unions

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Other Generic Top-Level Domains…Other TLDs later approved by ICANN include:

travel – travel industry jobs – 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_c1

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Country 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)

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Domain 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.net

Some of the things needed include:A valid email addressNames and addresses of the primary and secondary DNS serversA credit card (to pay online)

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DNS ComponentsName server – also known as DNS server

supports name-to-address and address-to-name resolution

Name resolver – also called DNS clientCan contact DNS server to lookup nameUsed by browsers, e-mail clients, and client utilities

such as ping

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DNS ServersThe two main DNS servers that define the Internet

are:Primary serversSecondary servers

Primary and secondary servers store the host names used on the Internet

The two main DNS servers that resolve domain names are:Caching serversForwarding servers

Caching and forwarding servers search the Internet for host names

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Primary and Secondary ServersPrimary Server

Defines the hosts for the domain Maintains the database for the domain

It has authority for the domainSecondary Server

Gets data from primary serverProvides fault tolerance and load distributionRequired for Internet domains

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Primary and Secondary Servers…If 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 changes

You can also split the serversISP has primary, you have secondaryYou have primary, ISP has secondary

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Primary and Secondary Servers…ISPs 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

faster

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Primary and Secondary Servers…You 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)

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Caching and Forwarding ServersCaching Server

Resolves host namesCaches (saves) the resultsAutomatically installed when DNS is installedNo configuration necessary

Forwarding ServerCaching server that has access to the Internet and forwards

traffic from other caching servers

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ZonesA 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 DNS

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Zones…Zones must be contiguous

admin.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 servers

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Zone File ConfigurationTwo 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

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DNS Configuration in Linux/etc/named.conf describes the files that configure

the zonesThere 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

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Starting 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 Linux

Add the command to start DNS to /etc/rc.d/rc.local

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Configuring 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 192.168.0.100

The following line associates this computer with the technowidgets.com domaindomain technowidget.com

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Testing 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)

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Name Resolution in WindowsNetBios (computer) names are broadcast to the local

networkThe WINS database has computer name to IP address

resolutionWindows uses Dynamic DNS

DNS is required for Active Directory Services

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