CMPN 369

1
CPSC441

• DNS Module
• Domain Name Service

2
Introduction

• Instead of using the numeric IP Address of the
  host it is possible to use the host name.
  Example
• www.google.ca
• acs3.acs.ucalgary.ca
• Translation of names to IP Addresses is done by
  nodes called Name Servers

3
DNS Name Space

• Hierarchy Structure
• ROOT

CA Country level Name Server
UCALGARY AB Region Name
Server
ACS SAIT Local Name
Server
IT
4
Domain Name Resolution

• User program issues the request
• Query to Name Server is formulated
• The name server checks if name in database.
• If not, ask the higher level Name Server
• Finally the user program gets IP Address or error

5
Subdomain versus Subnet

• Fully Qualified Domain Name. Example
• thunder.it.sait.ab.ca
• thunder - Actual host name
• it.sait.ab.ca - Part of the domain (subdomain)
• IP Address 142.110.16.7
• 142.110 - sait.ab.ca
• 16 - Subnet Number
• 7 - Host Number

6
Subdomain versus Subnet

• Subdomain can have many subnets
• Subnet can have many subdomains
• Command nslookup provides the conversion between
  Domain Names and IP Addresses

7
Generic Domains
8
The DNS Name Space

• A portion of the Internet domain name space.

9
Resource Records

• The principal DNS resource records types.

10
Resource Records

11
Name Servers

• Part of the DNS name space showing the division
  into zones.

12
Name Servers( flits.cs.vu.nl -linda.cs.yale.edu
)

• How a resolver looks up a remote name in eight
  steps.

13
NAMING SERVICES IN Unix or Linux     I.
Bypassing DNS /etc/hosts   127.0.0.1 localho
st.localdomain 192.168.66.1 sentinel 192.168
.66.99 zippo     II. Setting up DNS   Client
/etc/resolv.conf   nameserver xxx.xxx.xxx.xxx
(first DNS server) nameserver yyy.yyy.yyy.yyy
(second DNS server)     Server /etc/named.conf
. . zone "zone_name" type master file
"file_name" . .   "file_name" is the
name of the DNS database file  
14
DHCP versus DNS   DHCP can dynamically
change IP address of a node   DNS has static
assignment between IP addresses and
names     Solution Dynamic DNS (DDNS)   DDNS
cooperates with DHCP to maintain consistency