Web Server Administration Chapter 4 Name Resolution

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

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

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

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

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 is a fully qualified domain name (FQDN) We could create subdomains such as phx

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

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 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

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 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

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

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

Caching and Forwarding Servers

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

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

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

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!

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

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

Server DNS Configuration in Linux- File Structure Forward Lookup file /var/named/ named.technowidgets.com Reverse Lookup File /var/named/ named /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: web research mail

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

/etc/named.conf Creating a DNS for the technowidgets.com domain Default setup is for localhost 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

/etc/named.conf Also, we can add the following line zone “ in-addr.arpa” IN { type master; file “named ”; }; The domain begins at IN-ADDR.ARPA and has a substructure which follows the Internet addressing structure Example: data for Internet address is located at domain name IN-ADDR.ARPA This allows for reverse lookup for the domain It uses all or part of the network Make sure matches your hard drive number!

/var/named.technowidgets.com File Content Must be typed! IN SOA web1.technowidgets.com. admn.technowidgets.com. ( ; Serial ; Refresh ; Retry ; Expire ) ; Minimum IN NS web1 IN A IN MX 10 mail.technowidgets.com. web1 INA www INCNAMEweb1 research INA INMX 10mail mail INA

named File Content Must be typed! IN SOA web1.technowidgets.com. admn.technowidgets.com. ( ; Serial ; Refresh ; Retry ; Expire ) ; Minimum IN NS web1 20 IN PTR web1.technowidgets.com. 150IN PTR research.technowidgets.com. 200IN PTR mail.technowidgets.com.

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

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  Your HD! nameserver The following line associates this computer with the technowidgets.com domain domain technowidgets.com

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!

Troubleshooting DNS Linux dig hostname.com dig –silent xx ping Windows nslookup hostname.com nslookup –x xx Ipconfig ping

References: For Linux: For windows ServerHelp/5fe46cef-db12-4b78-94d2-2a0b62a28271.mspx ServerHelp/5fe46cef-db12-4b78-94d2-2a0b62a28271.mspx Read about IN-ADDR.ARPA domain