Web Server Administration

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

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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
           
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

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/etc/named.confCreating 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

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/var/named.technowidgets.com

• TTL 86400
• _at_ 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

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named.0.168.192

• TTL 86400
• _at_ 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-gtSettings-gtNetwork 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 DNSping

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

33
Troubleshooting DNSnslookup

• nslookup can display information from the DNS
  server

34
Troubleshooting DNSdig 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