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