This document discusses domain name system (DNS) configuration and troubleshooting. It describes DNS components like name servers, domains, and zones. It provides instructions for configuring DNS in Linux and Windows, including setting up primary and secondary servers with zone files. Troubleshooting tools like ping, nslookup, and dig are also covered.

1. Web Server Administration
Chapter 4
Name Resolution

2. 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
 Troubleshoot DNS
 Use WINS to resolve computer names in
Windows

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. How DNS Works

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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)

16. 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

17. Caching and Forwarding Servers

18. Zones
 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

19. Zones
 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

20. 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

21. Common DNS Records
DNS record Function
Address (A) Associates a host to an IP address.
Canonical name
(CNAME)
Creates an alias for a specified host.
Internet (IN) Identifies Internet records; precedes most DNS record
entries.
Mail Exchanger (MX) Identifies a server used for processing and delivering e-mail
for the domain.
Name server (NS) Identifies DNS servers for the DNS domain.
Pointer (PTR) Performs reverse DNS lookups. Resolves an IP address to a
host name.
Start of Authority
(SOA)
Identifies the DNS server with the most current information for
the DNS domain.

22. 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

23. /etc/named.conf
Creating a DNS for the technowidgets.com
domain
 Default setup is for localhost 127.0.0.1
 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

24. /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 192.168.0.0 network

25. /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 A 192.168.0.100
IN MX 10 mail.technowidgets.com.
web1 IN A 192.168.0.100
www IN CNAME web1
research IN A 192.168.0.150
IN MX 10 mail
mail IN A 192.168.0.200

26. 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.

27. 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

28. Configuring Client DNS in Linux
 Modify /etc/resolv.config
 The following line directs the client to
use the DNS server at 192.168.0.100
 nameserver 192.168.0.100
 The following line associates this
computer with the technowidgets.com
domain
 domain technowidgets.com

29. 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 192.168.0.10
 Reboot and ping www.technowidgets.com

30. 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

31. Finished DNS Configuration in
Windows

32. Troubleshooting DNS
ping
 ping displays name resolution even if the computer cannot be contacted

33. Troubleshooting DNS
nslookup
 nslookup can display information from the DNS server

34. Troubleshooting DNS
dig – available on Linux

35. Summary
 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