Host Name Resolution: Understanding DNS and WINS, Slides of Computer Networks

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Host Name Resolution DNS and WINS

Chapter Objectives

• Explain the process of hostname resolution to IP address on the Internet
• Describe the purpose of the HOSTS, LMHOSTS files
• Show how the HOSTS and LMHOSTS file could be modified to resolve abbreviated names to IP addresses

Name Resolution

• Resolve names to IP addresses and vice versa
  • www.calstatela.edu <-> 130.182.1.
• Names
  • TCP/IP host names
  • WINS names a.k.a. NetBIOS names

Finding an IP Address of a Domain

• ping www.ganesan.com
• tracert www.ganesan.com
  • Shows the number of hops to the destination

WINS or

NetBIOS

Names

Current Computer Names

• Only the TCP/IP host name is currently in widespread use
• The Windows based name or the NetBIOS name as it is known is not widely used anymore - This may be retained for compatibility with older systems

Internet Host Name Resolution

• First, a local file known as HOSTS is checked to

resolve the name to an IP address

• If a corresponding entry is not found in the HOST

file, the information is transmitted to a DNS server

for name resolution

• A cascade of DNS servers at different locations may

get involved in the resolution process

End of Module

Sample HOSTS File

Sample Entry in the HOSTS File

HOSTS File

• HOSTS file location
  • C:\Windows in Windows 9x
  • C:\WINNT\system32\drivers\etc in Windows NT
  • C:\Windows\system32\drivers\etc in Windows XP
• The file could be searched as well
• The extension of the file may be .SAM
• Note:
  • Store the file as “HOSTS” after modification with Notepad to avoid it being given a Notepad file extension

Redirection to DNS

• If there are no entries in the HOSTS file, the request is redirected to a DNS on the network
• Multiple DNSs may have to be consulted before the name is mapped to an IP address
• Domain names must also be registered with InterNIC or a similar organization

Domain Name Hosting: Another Example

courses.ganesan.com InterNIC points to the DNS server at ganesan.com DNS server at ganesan.com locates the host “course”

End of Module