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 2003
Troubleshoot DNS

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 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
A name such as is a fully qualified domain name (FQDN)
We could create subdomains such as phx

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, 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 Forwarding 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 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
Reverse lookup is described by named
Can be necessary for (SMTP) and security programs

23. /etc/named.conf Creating 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
Click what looks like a monitor at the bottom of the screen
type:
cd /etc
cp named.conf named.conf.org
gedit named.conf
add the above four lines being aware that it is case-sensitive

24. /etc/named.conf Also, we can add the following line
zone “ in-addr.arpa” IN {
type master;
file “named ”; };
This allows for reverse lookup for the domain
It uses all or part of the network

25. /var/named.technowidgets.com $TTL 86400
@ IN SOA web1.technowidgets.com. admn.technowidgets.com. (
; Serial
; Refresh
; Retry
; Expire
86400 ) ; Minimum
IN NS web1
IN A
IN MX 10 mail.technowidgets.com.
web1 IN A
www IN CNAME web1
research IN A
IN MX 10 mail
mail IN A

26. named
$TTL 86400
@ IN SOA web1.technowidgets.com. admn.technowidgets.com. (
; Serial
; Refresh
; Retry
; Expire
86400 ) ; Minimum
IN NS web1
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 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

28. 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

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
Reboot and ping

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