Transcript Host Name Resolution

CHAPTER
Host Name Resolution
DNS and WINS
© N. Ganesan, Ph.D., All rights reserved.
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
Module
Host Name Resolution Process
© N. Ganesan, Ph.D., All rights reserved.
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
A unique identifier known as the
Fully Qualified Domain Name (FQDN)
courses.ganesan.com
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
Module
Hosts File
© N. Ganesan, Ph.D., All rights reserved.
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 domain
points to the
DNS server
At Pacbell
Pacbell DNS
server points
to the DNS
server at
Ganesan.com
DNS server at
ganesan.com
locates the
host “course”
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
Module
LMHOST File
© N. Ganesan, Ph.D., All rights reserved.
Windows or NetBIOS Names
Domain
nanda
ganesan
kumar
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
Web Server
ganesan
Domain
Internet
nanda
kumar
NetBIOS Name Resolution
with LMHOSTS Entry
Access Path with LMHOSTS
Entry
Web Server
ganesan
Internet
nanda
kumar
Access Client
NetBIOS Name Resolution
without LMHOSTS Entry
IE5 searches for a web address match
and substitutes www.ganesan.com
Access Path without LMHOSTS
Entry
Web Server
ganesan
Internet
Access is through
the Internet.
nanda
kumar
Access Client
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
InterNIC
points to the
DNS server
At Pacbell
Pacbell DNS
server points
to the DNS
server at
Ganesan.com
DNS server at
ganesan.com
locates the
host “course”
End of Module
End of Chapter
© N. Ganesan, Ph.D., All rights reserved.