2440: 141
Web Site Administration
Domain Name System
Instructor: Enoch E. Damson

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The Domain Name System (DNS) is used to translate host names to IP addresses on the Internet
 Also called name resolution or address resolution
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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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 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
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 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)
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The root level domain is "."
 Significant in creating DNS files
Top-level domains identifies the most general part of the domain name
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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
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E.g. microsoft.com, uakron.edu
A subdomain is a further division of a second-level domain
 E.g. gozips.uakron.edu
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 Second-level domains, such as uakron.edu have control over naming within their domain
 E.g. sub-domains such as www3 and gozips below:
 www3.uakron.edu
 gozips.uakron.edu
 A Web server is commonly named www
 A name such as www.uakron.edu is a fully qualified domain name (FQDN)
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 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
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Internet Corporation for Assigned Names and Numbers (ICANN) is a non-profit organization that coordinates Internet unique identifiers
 http://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 resources
 http://www.iana.org
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The first original top-level domains (TLDs) that were available on the Internet included:
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 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
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 ICANN later approved other gTLDs in November 2000 below:
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 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
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Other TLDs later approved by ICANN include:
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 travel – travel industry jobs – the human resource management community mobi – consumers and providers of mobile products and services asia – Pan-Asia and Asia Pacific region xxx – 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 each
 Source: http://www.cnn.com/2011/TECH/web/06/20/domain.names.exp
lainer/index.html?hpt=hp_c1
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 There are about 250 country-specific TLDs
 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)
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Domain names are available on a first-come, first-served basis
Domain name availability may be verified from locations like:
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 http://www.dslreports.com/whois http://www.instantdomainsearch.com
http://www.godaddy.com
http://www.whois.net
Some of the things needed include:
 A valid email address
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Names and addresses of the primary and secondary DNS servers
A credit card (to pay online)
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 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
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 The two main DNS servers that define the Internet are:
 Primary servers
 Secondary servers
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Primary and secondary servers store the host names used on the Internet
 The two main DNS servers that resolve domain names are:
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Caching servers
Forwarding servers
 Caching and forwarding servers search the Internet for host names
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 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
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 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
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 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
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 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)
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 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
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 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
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 Zones must be contiguous
 admin.uakron.edu can be combined with uakron.edu
 admin.uakron.edu cannot be combined with student.uakron.edu
 There 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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 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
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 /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
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 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
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 Modify /etc/resolv.conf
 The following line directs the client to use the DNS server at the 192.168.0.100 IP address
 nameserver 192.168.0.100
 The following line associates this computer with the
technowidgets.com domain
 domain technowidget.com
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 Configure a Windows PC to use the DNS server
 Start->Settings->Network Connections
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Right-click on Local Area Connection and select Properties
Select Internet Protocol (TCP/IP) and click on Properties
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Change 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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 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
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