Domain Name System: DNS
TA: Awad A Younis Class: CS457
Fall 2014
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� Before DNS existence: • Users of ARPAnet used a hosts file called HOSTS.TXT
• Using this file, the conversion of the name to an IP Address was achieved by
� Downloading a large file contains all hosts and their IPs from a central
location
� Mapping between names and IPs Addresses
• As the internet grows this solution becomes impractical
• Domain Name Service (DNS) was created in 1983
� DNS: • Converts domain names to IP Addresses
� DNS is a distributed database
� No one computer is used to maintain a complete database of all of the domains
• Why DNS: routers and switches only understand the IP address
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• The top node, symbolized by a single dot, is known as the root.
• Below the root, you have the top-level domains like:
� com, net, org, mil, gov, edu, etc.
• How do you access your email at mail.example.org?
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• There are two components to DNS:
� Resolver: resides on client computers (Bingo!)
� Name server: answers questions about DN.
• It is listed in the resolver’s configuration file
It may not know how to access this site
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How can you bypass the DNS?
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� Example: • Suppose your computer wants to find the IP address of:
network-surveys.cr.yp.to.
• It contacts a series of DNS servers around the Internet.
• There are several DNS servers with information about network-surveys.cr.yp.to.
• A central root server (located at Internet HQ in Virginia) has the following data
in a file on disk:
.:198.41.0.4 : root server's IP address
&to:198.6.1.82 : .to server’s IP address
• Your computer also has 198.41.0.4 in a file on disk.
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� Example:
1. Your computer sends its question to the root server, and receives a response
from the root server's data:
network-surveys.cr.yp.to?
| Your | --------------------------> |198.41.0.4 |
|computer| <--------------- |root server|
&to:198.6.1.82
• The response &to:198.6.1.82 is a delegation.
• It says ``For information about .to, ask the DNS server at IP address 198.6.1.82'‘
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� Example:
• The DNS server at 198.6.1.82 has the following data in a file on disk: .to:198.6.1.82 &yp.to:131.193.178.160 2. Your computer sends its question to that DNS server, and receives a response: network-surveys.cr.yp.to? | Your | --------------------------> |198.6.1.82| |computer| <------------------------ |.to server | &yp.to:131.193.178.160 • The response &yp.to:131.193.178.160 is another delegation.
• It says ``For information about .yp.to, ask the DNS server at IP address
131.193.178.160''
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� Example: • The DNS server at 131.193.178.160 has the following data in a file on disk:
.yp.to:131.193.178.160
=network-surveys.cr.yp.to: 131.193.178.100
• Your computer sends its question to that DNS server, and receives a response:
network-surveys.cr.yp.to?
| Your | ------------------------------------------> |131.193.178.160|
|computer| <------------------------------------------ | .yp.to server |
=network-surveys.cr.yp.to: 131.193.178.100
• The response =network-surveys.cr.yp.to: 131.193.178.100, final answer
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� DIG: Domain Information Groper 1. Header Section:
2. Question Section: It shows what you asked dig to do
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� DIG: Domain Information Groper 3. Answer Section: It shows the answer for the query asked
4. Authority Section: It show who given the answer
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� DIG: Domain Information Groper
5. Additional Section: It show if any additional info that DNS server provided
� Project 3: • Client • MyReslover
� Makefile � Query.h � Response.h � Header.h
• Check up for: – www.cnn.commmm – DNS server time out – DNS server not found – No TCP/IP for big answer just stick with whatever UDP can handle
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Thank You
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