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Web Server Administration. Chapter 4 Name Resolution. Overview. Understand the domain name service (DNS) Identify the components of DNS Configure zone files Install and configure DNS in Linux Understand name resolution in Windows Install and configure DNS in Windows 2000 and 2003

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Web server administration

Web Server Administration

Chapter 4

Name Resolution


  • Understand the domain name service (DNS)

  • Identify the components of DNS

  • Configure zone files

  • Install and configure DNS in Linux

  • Understand name resolution in Windows

  • Install and configure DNS in Windows 2000 and 2003

  • Troubleshoot DNS

  • Use WINS to resolve computer names in Windows

Understanding the dns
Understanding the DNS

  • DNS is used to map host names to IP addresses on the Internet

    • Also called name resolution or address resolution

    • 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

  • A Microsoft Windows 2000 or Windows 2003 network uses 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


  • 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 namespaces
Domain Namespaces

  • The root level domain is "."

    • Significant in creating DNS files

  • Top-level domains include com, org, fr

    • More have been added in 2000

  • Second-level domains are often owned by companies and individuals

    • microsoft.com, devry.edu

  • A subdomain is a further division of a second-level domain

    • For devry.edu, there is phx.devry.edu

    • Not common

Domain namespaces1
Domain Namespaces

  • Second-level domains, such as devry.edu have control over naming within their domain

  • Create hosts such as www, ftp, bb

  • A name such as www.devry.edu is a fully qualified domain name (FQDN)

  • We could create subdomains such as phx

    • www.phx.devry.edu

New top level domains
New Top-Level Domains

  • .biz - businesses

  • .info - anyone can register

  • .name - must register first and last name

  • .pro - for professionals only

    • must provide proof

  • .aero, .museum, .coop are controlled by organizations

Host names
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

Dns components
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

Dns servers that define the internet
DNS Servers that Define the Internet

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

  • Caching and forwarding servers search the Internet for host names

Primary and secondary servers
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

Primary and secondary servers1
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

Primary and secondary servers2
Primary and Secondary Servers

  • ISP maintains 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

Primary and secondary servers3
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)

Resolve host names
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


  • A zone is a part of the domain namespace

  • For a domain as small as technowidgets.com, the domain name represents a single zone

  • For large organizations (such as IBM), subdomains can be divided into separately maintained zones

    • Each zone typically has a separate DNS


  • 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

Zone file configuration
Zone File Configuration

  • Forward Lookup

    • These zones contain entries that map names to IP addresses

  • Reverse Lookup

    • These zones contain entries that map IP addresses to names

Dns configuration in linux
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

Etc named conf creating a dns for the technowidgets com domain
/etc/named.confCreating a DNS for the technowidgets.com domain

  • Default setup is for localhost

  • In named.conf add the following line

    zone "technowidgets.com" {

    type master;

    file “named.technowidgets.com”;


  • This allows technowidgets.com to be resolved by /var/named/named.technowidgets.com

  • There can be multiple domains in a single named.conf file

Etc named conf

  • Also, we can add the following line

    zone “0.168.192.in-addr.arpa” IN {

    type master;

    file “named.0.168.192”;


  • This allows for reverse lookup for the domain

  • It uses all or part of the network

Var named technowidgets com

$TTL 86400

@ IN SOA web1.technowidgets.com. admn.technowidgets.com. (

2002072100 ; Serial

28800 ; Refresh

14400 ; Retry

3600000 ; Expire

86400 ) ; Minimum

IN NS web1


IN MX 10 mail.technowidgets.com.

web1 IN A

www IN CNAME web1

research IN A

IN MX 10 mail

mail IN A

Named 0 168 192

$TTL 86400

@ IN SOA web1.technowidgets.com. admn.technowidgets.com. (

2002072100 ; Serial

28800 ; Refresh

14400 ; Retry

3600000 ; Expire

86400 ) ; Minimum

IN NS web1

100 IN PTR web1.technowidgets.com.

150 IN PTR research.technowidgets.com.

200 IN PTR mail.technowidgets.com.

Starting dns in linux
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

Configuring client dns in linux
Configuring Client DNS in Linux

  • Modify /etc/resolv.config

  • The following line directs the client to use the DNS server at

    • nameserver

  • The following line associates this computer with the technowidgets.com domain

    • domain technowidgets.com

Test the dns
Test the DNS

  • Configure a Windows PC to use the DNS server

    • Start->Settings->Network and Dial-up Connections

    • Right-click on Local Area Connection and select Properties

    • Select Internet Protocol (TCP/IP) and click on Properties

    • Change DNS to

    • Reboot and ping www.technowidgets.com

Name resolution in windows
Name Resolution in Windows

  • NetBios (computer) names are broadcast to the local network

  • Starting with Windows NT, WINS database has computer name to IP address resolution

  • Windows 2000 introduces Dynamic DNS

    • DNS is required for Active Directory Services

  • DNS as described for Linux can also be configured

    • Wizards guide you through the configuration

Troubleshooting dns ping
Troubleshooting DNSping

  • ping displays name resolution even if the computer cannot be contacted

Troubleshooting dns nslookup
Troubleshooting DNSnslookup

  • nslookup can display information from the DNS server

Troubleshooting dns dig available on linux
Troubleshooting DNSdig – available on Linux


  • DNS is an application that translates names to IP addresses and IP addresses to names

  • Organized in a hierarchical structure

  • Servers come in many forms: primary, secondary, caching, forwarding

  • To configure DNS, set up a forward and reverse zone

  • Use ping, nslookup, and dig to troubleshoot DNS