Hostname Resolution
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Transcript of Hostname Resolution
© N. Ganesan, Ph.D., All
rights reserved.
CHAPTER
Host Name ResolutionDNS 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
© N. Ganesan, Ph.D., All
rights reserved.
Module
Host Name Resolution Process
Name Resolution
• Resolve names to IP addresses and vice versa– www.calstatela.edu <-> 130.182.1.60
• 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
TCP/IP Host
Name Example
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 Names
.com .edu .org Etc.
ganesan.com
courses.ganesan.com
A unique identifier known as theFully Qualified Domain Name (FQDN)
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
© N. Ganesan, Ph.D., All
rights reserved.
Module
Hosts File
Sample HOSTS File
Sample Entry in the HOSTS File
Host Name Resolution Example
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
DNS Perspective of Name Resolution
courses.ganesan.com
.com root domainpoints to the DNS serverAt Pacbell
Pacbell DNSserver pointsto the DNSserver at
Ganesan.com
DNS server at ganesan.comlocates the
host “course”
Domain Name Hosting: Another Example
courses.ganesan.com
InterNICpoints to the DNS server
at ganesan.com
DNS server at ganesan.comlocates the
host “course”
End of Module
© N. Ganesan, Ph.D., All
rights reserved.
Module
LMHOST File
Windows or NetBIOS Names
kumarnanda
ganesanDomain
Uniform Naming Convention (UNC)
• Applies to finding a resource on a local network• \\windowsname\folder\file• An example of windowsname could be a server
name• \\kumar\sales\annual.doc• Note: FQDN applies to the Internet where a
website, for example, is located using this name • Find the FQDN of your computer, if it is
connected to the Internet
Windows Name Resolution
• First a local file known as LMHOSTS is checked to resolve the name to an IP
• If a corresponding entry is not found in the HOST file, the information is transmitted to a WINS server for name resolution
• WINS– Windows Internet Name Service
Sample Partial LMHOSTS File
Inclusion of lmhosts files from other computers.
Sample Entry in LM HOSTS File
Intranet Example
kumarnanda
ganesanDomain
Internet
Web Server
NetBIOS Name Resolution with LMHOSTS Entry
Access Path with LMHOSTS Entry
kumarnanda
ganesan
Internet
Web Server
Access Client
NetBIOS Name Resolution without LMHOSTS Entry
IE5 searches for a web address matchand substitutes www.ganesan.com
Access Path without LMHOSTS Entry
kumarnanda
ganesan
Internet
Web Server
Access Client
Access is through the Internet.
IE5 Search for Web Address Match
LMHOSTS File
• LMHOSTS file location– C:\Windows in Windows 9x– C:\WINNT\system32\drivers\etc– C:\Windows\system32\drivers\etc
• The extension of the file is .SAM• Note:
– Store the file as “LMHOSTS” after modification with Notepad to avoid it being given a Notepad file extension
Redirection to WINS
• If there are no entries in the LMHOSTS file, the request is redirected to a WINS server on the network
• In the last example, there was no WINS server on the LAN– Therefore, IE5 serarched for a web
matching web address
WINS Perspective of Name Resolution
courses.ganesan.com
InterNICpoints to the DNS serverAt Pacbell
Pacbell DNSserver pointsto the DNSserver at
Ganesan.com
DNS server at ganesan.comlocates the
host “course”
© N. Ganesan, Ph.D., All
rights reserved.
End of Module
End of Chapter