COMP210

• DNS Module

• Domain Name Service

Dr Ahmad Al-Zubi

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

DNS Name Space

• Hierarchy Structure

ROOT

CA Country level Name Server

UCALGARY AB Region Name Server

ACS SAIT Local Name Server

IT

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

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

Subdomain versus Subnet

• Subdomain can have many subnets

• Subnet can have many subdomains

• Command nslookup provides the conversion between Domain Names and IP Addresses

Generic Domains

DomainName

comedugovmilnetorgcountry

Meaning

CommertialEducationalGovernmentMilitaryMajor ProvidersNon-Profit2-letters code

The DNS Name Space

A portion of the Internet domain name space.

Resource Records

The principal DNS resource records types.

Resource Records

Name Servers

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

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

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

NAMING SERVICES IN Unix or Linux  I. Bypassing DNS: /etc/hosts 

127.0.0.1localhost.localdomain

192.168.66.1 sentinel192.168.66.99 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

 

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