Web server administration chap04

Web Server Administration
Chapter 4
Name Resolution


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


Clients
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On your PC, the TCP/IP configuration contains the
address(es) of your DNS server(s)

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Whenever you use a URL, whether in a browser, or a
utility such as ping, DNS servers are used


Domain Namespaces
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The root level domain is "."
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Top-level domains include com, org, fr
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More have been added in 2000

Second-level domains are often owned by
companies and individuals
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Significant in creating DNS files

microsoft.com, devry.edu

A subdomain is a further division of a secondlevel domain
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For devry.edu, there is phx.devry.edu
Not common


Domain Namespaces
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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
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www.phx.devry.edu

New Top-Level Domains
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.biz - businesses

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.info - anyone can register

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.name - must register first and last name

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.pro - for professionals only
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must provide proof

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


Host Names
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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


How DNS Works


DNS Components
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Name server – also known as DNS server
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supports name-to-address and
address-to-name resolution

Name resolver – also called DNS client
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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
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Primary and secondary servers store the host names
used on the Internet

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Caching and forwarding servers search the Internet for
host names


Primary and Secondary
Servers
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Primary Server
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Defines the hosts for the domain
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Maintains the database for the domain

It has authority for the domain

Secondary Server
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Gets data from primary server
Provides fault tolerance and load
distribution
Required for Internet domains


Primary and Secondary
Servers
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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
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You contact them for changes

You can also split the servers
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ISP has primary, you have secondary
You have primary, ISP has secondary


Primary and Secondary
Servers
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ISP maintains DNS

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You have to send changes to ISP

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You have the secondary server which gets updates from
the primary server

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Your users reference your secondary server which is faster

Primary and Secondary
Servers
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You have complete control over DNS

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You can make changes whenever you want

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If your primary DNS goes down, the secondary will
continue to function (but not indefinitely)


Resolve Host Names
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Caching Server
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Resolves host names
Caches (saves) the results

Automatically installed when DNS is installed
No configuration necessary

Forwarding Server
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Caching server that has access to the
Internet and forwards traffic from other
caching servers


Caching and Forwarding Servers


Zones
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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
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Each zone typically has a separate DNS


Zones
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Zones must be contiguous
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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
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Forward Lookup
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These zones contain entries that map
names to IP addresses

Reverse Lookup
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These zones contain entries that map
IP addresses to names


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.


DNS Configuration in Linux
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/etc/named.conf describes the files that
configure the zones
There are two primary files that it describes
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Forward lookup is described by
named.technowidgets.com
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It has the host names and how to handle e-mail

Reverse lookup is described by named.0.168.192
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Can be necessary for e-mail (SMTP) and security
programs


/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”;
};
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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
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Also, we can add the following line
zone “0.168.192.in-addr.arpa” IN {
type master;
file “named.0.168.192”;
};

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This allows for reverse lookup for the
domain
It uses all or part of the 192.168.0.0
network

/
var/named.technowidgets.co
$TTL
86400
@
m( 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