Updated: May 17, 2017

Host Name Resolution Methods Explained

When you type an Internet address into a web browser the web browser needs to convert that web address into an IP address.

To do that is uses the the name resolution processes provided by the host machine.

There are several ways that the host machine can resolve a domain name. The main ones are:

  • hosts file lookup
  • DNS lookup

Generally a host will try multiple methods until it succeeds or runs out of methods to try,and then it fails.

The order in which it tries this method is a host parameter that can be changed.

In Linux this is done in the /etc/nsswitch.conf file.

Name resolution and Host Type

There are three operating systems in common use on home and corporate networks. They are

  • Microsoft Windows
  • Apple OSes
  • Linux

Early Windows networks used the Netbeui (NetBIOS) protocol which had its own name resolution methods.

Likewise Apple also had their own networking protocols and name resolution methods.

The Internet was built on Linux (Unix) and TCP/IP which used the hosts file and DNS as the main name resolution methods.

Microsoft and Apple moved from their proprietary networking protocols and standardized on TCP/IP, and in doing so adopted the hosts file and DNS resolution methods.

However they also kept their old methods, and modified them to work over TCP/IP.

Windows And Apple Name Resolution Methods

Windows specific name resolution methods are:

  • NetBIOS name cache
  • LMhosts
  •  Wins

Apple specific name resolution methods are:

  • NBP (network binding protocol)

Name Resolution Order and Application

The name resolution order can also be affected by the type of application making the request.

On Windows machines, traditional NetBIOS application use NetBIOS name resolution methods before they use the hosts file and DNS. See here

However SMTP, FTP and other traditional Internet protocols and application use hosts and DNS. See here

Viewing and Clearing the DNS Cache- Windows

On Windows machines you can see the contents of the DNS cache and clear it using the ipconfig command.

To clear the cache use:

command ipconfig/flushdns

flushdns

To clear the cache use:

command ipconfig/displaydns

displaydns

Viewing the NetBIOS Name Cache

To View the  NetBIOS Name Cache use the nbtstat command nbtstat -c

nbtstat-cache

See this Technet article for a more detailed look at nbtstat.

Common Questions and Answers

Q- What is the LMhosts File and where is it stored?

A- The LMhosts file is found on Windows machines and is used for NetBIOS name to IP address mapping similar to the hosts File. It is found in the same folder as the hosts file which on windows XP,windows 7  it is located in c:\windows\system32\drivers\etc\,

Q- What is WINS?

A- Just as LMhosts is the Windows equivalent to hosts, Wins is the Windows equivalent to DNS. I don’t believe it is used anymore.

Q- Can I tell which method resolved the host name?

A- No

Related Tutorials and Resources:

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