© N. Ganesan, Ph.D., All rights reserved. CHAPTER 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

© 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 Names –TCP/IP host names –WINS names a.k.a. NetBIOS names

Finding an IP Address of a Domain ping tracert –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.orgEtc. ganesan.com courses.ganesan.com A unique identifier known as the Fully 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 organizationInterNIC

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

© N. Ganesan, Ph.D., All rights reserved. Module LMHOST File

Windows or NetBIOS Names kumarnanda ganesan Domain

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 ganesan Domain 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 match and substitutes

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 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”

© N. Ganesan, Ph.D., All rights reserved. End of Module End of Chapter