comp210 dns module domain name service dr ahmad al-zubi
TRANSCRIPT
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COMP210
• DNS Module
• Domain Name Service
Dr Ahmad Al-Zubi
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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
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DNS Name Space
• Hierarchy Structure
ROOT
CA Country level Name Server
UCALGARY AB Region Name Server
ACS SAIT Local Name Server
IT
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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
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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
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Subdomain versus Subnet
• Subdomain can have many subnets
• Subnet can have many subdomains
• Command nslookup provides the conversion between Domain Names and IP Addresses
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Generic Domains
DomainName
comedugovmilnetorgcountry
Meaning
CommertialEducationalGovernmentMilitaryMajor ProvidersNon-Profit2-letters code
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The DNS Name Space
A portion of the Internet domain name space.
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Resource Records
The principal DNS resource records types.
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Resource Records
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Name Servers
Part of the DNS name space showing the division into zones.
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Name Servers( flits.cs.vu.nl ->linda.cs.yale.edu )
How a resolver looks up a remote name in eight steps.
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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
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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