Web server administration chap04

Understanding the DNSon 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

Web Server Administration

Chapter 4 Name Resolution

and 2003

Windows

Understanding the DNS

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

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

 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

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

 biz - businesses

 info - anyone can register

 name - must register first and last name

 pro - for professionals only

 aero, museum, coop are controlled by organizations

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

How DNS Works

DNS Components

 Name server – also known as DNS server

address-to-name resolution

 Name resolver – also called DNS client

name

client utilities such as ping and tracert

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

 Defines the hosts for the domain

 Maintains the database for the domain

 It has authority for the domain

 Gets data from primary server

 Provides fault tolerance and load distribution

Required for Internet domains

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

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

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

 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

Caching and Forwarding 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

 admin.devry.edu can be combined with

devry.edu

 admin.devry.edu cannot be combined with student.devry.edu

in each zone (plus a secondary server)

DNS servers

Zone File Configuration

Creates an alias for a specified host

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

to a host name.

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

Creating a DNS for the technowidgets.com domain

 Default setup is for localhost 127.0.0.1

 In named.conf add the following line

var/named.technowidgets.co m

 Add the command to start DNS to

/etc/rc.d/rc.local

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

 DNS is required for Active Directory Services

 DNS as described for Linux can also be

configured

Finished DNS Configuration in Windows

Troubleshooting DNS ping

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

Troubleshooting DNS

nslookup

 nslookup can display information from the DNS server

Troubleshooting DNS

dig – 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