Domain Name Service


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  • Click what looks like a monitor at the bottom of the screen
    cd /etc
    cp named.conf
    gedit named.conf
    add the above four lines being aware that it is case-sensitive
  • Domain Name Service

    1. 1. Web Server Administration Chapter 4 Name Resolution
    2. 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. 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. 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. 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. 6. Domain Namespaces  Second-level domains, such as have control over naming within their domain  Create hosts such as www, ftp, bb  A name such as is a fully qualified domain name (FQDN)  We could create subdomains such as phx 
    7. 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. 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. 9. How DNS Works
    10. 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. 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. 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. 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. 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. 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. 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. 17. Caching and Forwarding Servers
    18. 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. 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. 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. 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 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.
    22. 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 e-mail  Reverse lookup is described by named.0.168.192  Can be necessary for e-mail (SMTP) and security programs
    23. 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
    24. 24. /etc/named.conf  Also, we can add the following line zone “” IN { type master; file “named.0.168.192”; };  This allows for reverse lookup for the domain  It uses all or part of the network
    25. 25. /var/ $TTL 86400 @ IN SOA ( 2002072100 ; Serial 28800 ; Refresh 14400 ; Retry 3600000 ; 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. 26. named.0.168.192 $TTL 86400 @ IN SOA ( 2002072100 ; Serial 28800 ; Refresh 14400 ; Retry 3600000 ; Expire 86400 ) ; Minimum IN NS web1 100 IN PTR 150 IN PTR 200 IN PTR
    27. 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. 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. 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. 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. 31. Finished DNS Configuration in Windows
    32. 32. Troubleshooting DNS ping  ping displays name resolution even if the computer cannot be contacted
    33. 33. Troubleshooting DNS nslookup  nslookup can display information from the DNS server
    34. 34. Troubleshooting DNS dig – available on Linux
    35. 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