1. LINUX ADMINISTRATION 1

2. UNIT 4
CHAPTER-2 2

3. CHAPTER 1 : DOMAIN NAME SYSTEM
Understanding DNS
Each time you type a Web site‘s address into your browser, the Domain Name System (DNS) goes to work.
Domain names are organized in subordinate levels (subdomains) of the DNS root domain, which is nameless.
The first-level set of domain names are the top-level
domains (TLDs),
including the generic top-level domains (gTLDs), such as the prominent domains com, net and org, and the
country code top-level domains (ccTLDs). 3

4. When you type in a host name, your system uses its resources to resolve names into IP addresses.
One of these files is /etc/nsswitch.conf (nsswitch means name service switch), which contains a line telling the system where to look for host information. 4

5. After the system looks in the hosts file and fails to find the address, the next file checked is
/etc/resolv.conf.
This file contains the IP addresses of computers that are known as Domain Name Servers, and these are listed in /etc/resolv.conf as just name servers. 5

6. INSTALLING THE SOFTWARE
Install The RPM version of BIND(Berkeley Internet
Name Daemon)
Installing the package installs all the files necessary to set up DNS.
The installation creates a directory /var/named and places two files,
/var/named/named.ca and
/var/named/named.local here.
Two files are created in the /etc directory:
/etc/named.conf and
/etc/named.boot.
Four files are created in /usr/sbin
The file /usr/sbin/named is the name server daemon
named-boot is a Perl script that converts named.boot files to named.conf files
named-xfer is a transfer program for external zone files;
rndc is the name server daemon control program. (start|stop|restart) 6

7. UNDERSTANDING TYPES OF DOMAIN SERVERS
nslookup command to search for the root name server for .edu
1st .edu.
2nd Muhlenberg.edu.
3rd www. Muhlenberg.edu. 7

8. THE THREE TYPES OF LOCAL DOMAIN
NAME SERVERS
Master
The master contains all the information about the domain and supplies this information when requested
Slave
The slave is intended as a backup in case the master server goes down or is not available.
Caching
The caching server remembers the domains that have been accessed.
Use of a caching server speeds up searches since the domain information is already stored in memory 8

9. EXAMINING SERVER CONFIGURATION FILES
You need five files to set up the named server
The three required files are
named.conf — found in the /etc directory
contains global properties and sources of configuration files
named.ca — found in /var/named
contains the names and addresses of root servers.
named.local — found in /var/named
file provides information for resolving the loopback address
for the localhost.
The two files required for the master domain server are
zone — this file contains the names and addresses of servers and workstations in the local domain and maps names to IP addresses
reverse zone — this file provides information to map IP addresses to names 9

10. Named.conf 10

11. HOSTS.DB 11

12. HOSTS.REV 12

13. SOA — START OF AUTHORITY
The start of authority (SOA) is the first line in the zone file.
NS — NAME SERVERS IN THIS DOMAIN
Shows the names of the name servers.
A — THE IP ADDRESS FOR THE NAME
Shows the IP address for the name servers.
PTR — POINTER FOR ADDRESS NAME MAPPING
Used to point to the name servers
CNAME — CANONICAL NAME
Shows the real name of the host
MX RECORD — MAIL EXCHANGE RECORD
The MX record specifies the mail servers for the domain. 13

14. The named.ca file The named.local file
The first zone file is known as the cache file, and it references a file called named.ca, which contains information about the world‘s root name servers. This information changes and needs to be updated periodically.
The named.local file
The next zone file contains information about the localhost. The file referenced here is named.local and contains information about the local domain 14

15. USING DNS TOOLS nslookup host dig
Nslookup is one of several programs that can be used to obtain information about your name servers.
host
Host enables you to find an IP address for the specified domain name
dig
Dig can be used for debugging and obtaining other
useful information
Forward lookup
dig siddhesh.weit
reverse lookup
 dig –x 15

16. THANK YOU 16