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 microsoft.com, ccsu.edu A subdomain is a further division of a second- level domain For ccsu.edu, there is phx.ccsu.edu Not common

6. Domain Namespaces Second-level domains, such as ccsu.edu have control over naming within their domain Create hosts such as www, ftp A name such as www.ccsu.edu is a fully qualified domain name (FQDN) We could create subdomains such as phx www.phx.ccsu.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

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 In a simple environment, the ISP will have the primary and secondary DNS servers ISP maintains DNS You have to send changes to ISP You have the secondary server which gets updates from the primary server

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. 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

16. Caching and Forwarding Servers

17. 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

18. Zones Zones must be contiguous admin.ccsu.edu can be combined with ccsu.edu admin.ccsu.edu cannot be combined with student.ccsu.edu There must be one primary DNS server in each zone (plus a secondary server) Each zone can have multiple secondary DNS servers

19. 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

20. DNS Configuration in Linux Projects 4-1 through 4-3 Projects 4-4 deals with multiple domains Lab Projects Objective: Upon completion you must show using the dig command you get the correct IP and corresponding domain name!

21. Review of Zoning 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 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

22. DNS Configuration in Linux File Structure /etc/named.conf File name: /etc/resolve.conf File name: Client DNS ConfigurationServer DNS Configuration Adding nameserver and domain Nameserver: Corresponding IP address Domain: Corresponding domain name Name resolution

23. Server DNS Configuration in Linux- File Structure Forward Lookup file /var/named/ named.technowidgets.com Reverse Lookup File /var/named/ named.0.168.192 /etc/named.conf File name: 1- Configure this file so it reads the proper lookup files below 2- Create these two files for both forward and reverse lookup files Defines other subdomains such as: research.technowidgets.com. mail.technowidgets.com. Defines other subdomains such as: web1192.168.0. 20 research192.168.0.150 mail192.168.0.200

24. 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 Reverse lookup is described by named.0.168.192

25. /etc/named.conf Creating a DNS for the technowidgets.com domain Default setup is for localhost 127.0.0.1 This is shown in figure 4-7 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

26. /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”; }; The domain begins at IN-ADDR.ARPA and has a substructure which follows the Internet addressing structure Example: data for Internet address 10.2.0.52 is located at domain name 52.0.2.10.IN-ADDR.ARPA This allows for reverse lookup for the domain It uses all or part of the 192.168.0.20 network Make sure 192.168.0.20 matches your hard drive number!

27. /var/named.technowidgets.com File Content Must be typed! $TTL86400 @ IN SOA web1.technowidgets.com. admn.technowidgets.com. ( 2002072100 ; Serial 28800 ; Refresh 14400 ; Retry 3600000 ; Expire 86400 ) ; Minimum IN NS web1 IN A 192.168.0.20 IN MX 10 mail.technowidgets.com. web1 INA192.168.0. 20 www INCNAMEweb1 research INA192.168.0.150 INMX 10mail mail INA192.168.0.200

28. named.0.168.192 File Content Must be typed! $TTL86400 @ IN SOA web1.technowidgets.com. admn.technowidgets.com. ( 2002072100 ; Serial 28800 ; Refresh 14400 ; Retry 3600000 ; Expire 86400 ) ; Minimum IN NS web1 20 IN PTR web1.technowidgets.com. 150IN PTR research.technowidgets.com. 200IN PTR mail.technowidgets.com.

29. Starting DNS in Linux Useful commands 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 To make DNS start when you boot Linux Add the above commands to start DNS to /etc/rc.d/rc.local

30. Configuring Client DNS in Linux Objective: How IP addresses are corresponding to domain names Modify /etc/resolv.config The following line directs the client to use the DNS server at 192.168.0.20  Your HD! nameserver 192.168.0.20 The following line associates this computer with the technowidgets.com domain domain technowidgets.com

31. Troubleshooting DNS dig – available on Linux Upon Completion; you must be able to get this! -- Must match your HD! Use dig command to check the results!

32. Troubleshooting DNS Linux dig hostname.com dig –silent 192-168- 0-xx ping Windows nslookup hostname.com nslookup –x 192- 168.0.xx Ipconfig ping

33. References: For Linux: http://www.siliconvalleyccie.com/linux-hn/dns-static.htm For windows http://www.microsoft.com/technet/prodtechnol/windowsserver2003/library/ ServerHelp/5fe46cef-db12-4b78-94d2-2a0b62a28271.mspx http://www.microsoft.com/technet/prodtechnol/windowsserver2003/library/ ServerHelp/5fe46cef-db12-4b78-94d2-2a0b62a28271.mspx Read about IN-ADDR.ARPA domain http://www.freesoft.org/CIE/RFC/1035/36.htm