1. The University of Akron Summit College Business Technology Dept.
2440: 141 Web Site Administration
Domain Name System
Instructor: Enoch E. Damson

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
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 is a fully qualified domain name (FQDN)
Domain Name System

7. 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

8. ICANN and IANA
Internet Corporation for Assigned Names and Numbers (ICANN) is a non-profit organization that coordinates Internet unique identifiers
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
Domain Name System

9. Top-Level Domains
The first original top-level domains (TLDs) 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
Domain Name System

10. Other Generic Top-Level Domains
ICANN later approved other gTLDs in November 2000 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

11. Other Generic Top-Level Domains…
Other TLDs later approved by ICANN include:
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:
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:
Domain Name System

12. Country Top-Level Domains
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)
Domain Name System

13. Domain Name Registration
Domain names are available on a first-come, first-served basis
Domain name availability may be verified from locations like:
Some of the things needed include:
A valid address
Names and addresses of the primary and secondary DNS servers
A credit card (to pay online)
Domain Name System

14. 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, clients, and client utilities such as ping
Domain Name System

15. DNS Servers 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

16. 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

17. 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

18. 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

19. 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

20. Caching and Forwarding Servers
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

21. 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

22. Zones… 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
Domain Name System

23. 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

24. 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
Reverse lookup is described by named
Can be necessary for (SMTP) and security programs
Domain Name System

25. Starting DNS in Linux To start DNS To restart DNS To stop 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

26. Configuring Client DNS in Linux
Modify /etc/resolv.conf
The following line directs the client to use the DNS server at the IP address
nameserver
The following line associates this computer with the technowidgets.com domain
domain technowidget.com
Domain Name System

27. Testing the DNS in Windows
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 an IP address (to a domain name)
Reboot the computer and ping a domain name mapped to the IP address above (such as ping
Domain Name System

28. 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