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Web Server Administration

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Presentation on theme: "Web Server Administration"— Presentation transcript:

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, A subdomain is a further division of a second-level domain For, there is Not common

6 Domain Namespaces Second-level domains, such as 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, 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 can be combined with cannot be combined with 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 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 domain
Default setup is for localhost In named.conf add the following line zone "" { type master; file “”; }; This allows to be resolved by /var/named/ 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 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 { type master; file “named ”; }; This allows for reverse lookup for the domain It uses all or part of the network

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

26 named $TTL 86400 @ IN SOA ( ; Serial ; Refresh ; Retry ; Expire 86400 ) ; Minimum IN NS web1 IN PTR 150 IN PTR 200 IN PTR

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 domain domain

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

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